Germanium-silicon-tin (GeSiSn) heterojunction bipolar transistor devices

ABSTRACT

The methods of manufacture of GeSiSn heterojunction bipolar transistors, which include light emitting transistors and transistor lasers and photo-transistors and their related structures are described herein. Other embodiments are also disclosed herein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent ApplicationNo. 62/677,180, filed May 29, 2018, the contents of which are herebyincorporated by reference.

Further, this application is a continuation-in-part of U.S.Non-Provisional patent application Ser. No. 15/606,965, filed May 26,2017. Application Ser. No. 15/606,965 is a continuation of U.S.Non-Provisional patent application Ser. No. 14/504,114, filed Oct. 1,2014, now U.S. Pat. No. 9,666,702, which is a continuation-in-part ofU.S. Non-Provisional application Ser. No. 14/217,022, filed Mar. 17,2014, now U.S. Pat. No. 9,437,772. Application Ser. No. 14/217,022claims benefit of U.S. Provisional Patent Application No. 61/885,434,filed Oct. 1, 2013, and of U.S. Provisional Patent Application No.61/800,175, filed Mar. 15, 2013. U.S. Non-Provisional patent applicationSer. Nos. 15/606,965, 14/504,114 and 14/217,022, U.S. Provisional PatentApplication No. 61/885,434, and U.S. Provisional Patent Application No.61/800,175 are incorporated herein by reference in their entirety.

BACKGROUND

Heterojunction transistors, including heterojunction bipolar transistorsare desirable for use as electronic and photonic devices.

BRIEF SUMMARY

This description relates generally to semiconductor devices, and moreparticularly to advanced heterojunction bipolar transistors (HBT), lightemitting transistors (LET), transistor lasers, photo-diodes,photo-transistors and microelectronic devices. These devices may utilizequantum wells (QW) and quantum (QD) regions.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a general configuration of a bipolar transistor as a threeterminal device in its two constituent forms NPN and PNP.

FIG. 2 shows a general cross-sectional device depiction of a bipolartransistor in a vertical stack geometry.

FIG. 3 shows a flat band energy diagram for three typical heterojunctionsituations between the emitter and base materials: type I, type II, nearzero conduction band offset.

FIG. 4 shows a flat band energy diagram for three typical heterojunctionsituations between the base and collector materials: type I, type II,near zero conduction band offset.

FIG. 5 shows a flat band edge diagram for an NPN transistor for possiblyenhanced transport.

FIG. 6 shows a flat band edge diagram for a PNP transistor for possiblyenhanced transport.

FIG. 7 shows a general configuration of an injection laser diode, with aquantum well or quantum dot active region.

FIG. 8 shows a flat band energy diagram of a general configuration of aseparate confinement heterostructure laser with an active QW or QDregion which can be of the type I heterojunction band alignment.

FIG. 9 shows an example of a cut away device depiction of an edgeemitting injection diode laser.

FIG. 10 shows an example of a cross-sectional device depiction of avertical cavity surface emitting laser (VCSEL), where light is comingout of the bottom, but could be designed so that light comes out of thetop. Also this can also depict a light emitting transistor.

FIG. 11 shows a simple diagram of an NPN transistor laser or lightemitting transistor showing the three terminal device configuration witha corresponding free carrier type designation, with a quantum well orquantum dot active region in the base.

FIG. 12 shows a possible cross-sectional device depiction of an NPN edgeemitting transistor laser or light emitting transistor (LET) structure.

FIG. 13 shows an example of a possible cross-sectional device depictionof an NPN VCSEL transistor laser or light emitting transistor (LET)where light is coming out of the top, but also could be designed so thatlight comes out of the bottom.

FIG. 14 shows energy band structure diagrams for Si, Ge and Snsemiconductor materials.

FIG. 15 shows a graph of collector current density J_(C) vs. turn-onvoltages (V_(BE)) of various HBT material systems. The GeSiSn alloysemiconductor can have a wide range of turn on voltages less than 1.0 V.

FIG. 16 shows the hole concentration of GeSn films as a function of Sn%, as measured by Hall effect. High hole concentrations can be achievedby GeSn.

FIG. 17 shows a representative possible graph showing GeSiSn (latticematched to GaAs) bandgap energy vs. Sn %.

FIG. 18 shows the bandgap energy of relaxed GeSn vs. Sn %. GeSn bandgapstarts indirect and transitions to direct at higher Sn %.

FIG. 19 shows a formation of quantum dot structures resulting fromself-assembled GeSiSn quantum dots by the Stranski-Krastanov (SK) methodthat transitions from two dimensional planar growths to island growth.

FIG. 20 shows a flat band energy diagram of a GeSiSn quantum dot (QD) toSi which can be of type II or type I heterojunction band alignment.

FIG. 21 shows a possible range of emission wavelengths that areachievable in a type II GeSn quantum dot heterostructure with Sibarriers. This possible data is for low Sn % GeSn alloys.

FIG. 22 shows a flat band energy diagram of GeSiSn (low Sn %) quantumdot (QD) or quantum well (QW) with SiGe barriers which can be of type Ialignment.

FIG. 23 shows a methodology of planar growth of a GeSiSn quantum well QWregion on top of a GaAs barrier layer, and then growth of another GaAsbarrier layer on top of the GeSiSn QW layer.

FIG. 24 shows a flat band energy band type I alignment of a GeSiSn QWwith a GaAs barrier.

FIG. 25 shows a general flat band energy diagram of an NPN GeSiSn doubleheterojunction bipolar transistor.

FIG. 26 shows a flat band energy diagram of an NPN HBT with acompositionally graded GeSiSn base. The compositionally gradedGeSiSn—GeSn base layer can comprise at the emitter-base interface alattice matched or near latticed matched or strainedGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAs, where the GeSiSn may becompositionally graded by reducing the Si content and increasing Gecontent to GeSn at the base-collector interface. The grading range cango from GeSiSn at the emitter-base junction to GeSn at thebase-collector junction various compositions and may result in fieldenhancement in the base region.

FIG. 26A shows a flat band energy diagram of an NPN HBT with GeSi base.

FIG. 27 shows a resulting flat band energy diagram of a GeSiSn quantumwell or quantum dot material placed in the base region of aheterojunction transistor.

FIG. 28 shows a flat band energy diagram of a GeSiSn quantum well (QW)or quantum dot (QD) where a barrier has been graded from a base materialto a GeSiSn active region.

FIG. 29 illustrates an exemplary flat band energy diagram of an NPNstructure of a GaAs emitter-GeSiSn base-GaAs collector symmetric doubleHBT.

FIG. 30 shows an exemplary cross-sectional device depiction embodimentof an NPN GaAs—GeSiSn—GaAs symmetric double HBT.

FIG. 31 illustrates an exemplary flat band energy diagram of an NPNstructure of a GaAs emitter-compositionally graded GeSiSn—GeSn base-GaAscollector double heterojunction transistor. The compositionally gradedGeSiSn—GeSn base layer can comprise at the emitter-base interface alattice matched or near-latticed matched or strainedGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAs, where the GeSiSn may becompositionally graded by reducing the Si content and increasing Gecontent to GeSn at the base-collector interface. The grading range cango from GeSiSn at the emitter-base junction to GeSn at thebase-collector junction various compositions and may result in fieldenhancement in the base region.

FIG. 31A shows a flat band energy diagram of a GaAs emitter-GeSibase-GaAs collection symmetric double HBT. The GeSi can be latticematched or near latticed matched or coherently strained to the GaAslayers.

FIG. 32 shows an exemplary flat band energy diagram of an NPN transistorlaser or light emitting transistor (LET) structure with a GeSn QW or QDactive region in a GeSiSn P-type base/barrier material 3200.

FIG. 33 shows a possible cross-sectional device depiction of an NPNtransistor laser or light emitting transistor structure with a GeSn QWor QD active region in a GeSiSn P-type base/barrier material 3300.

FIG. 34 shows an exemplary flat band energy diagram of an NPN transistorlaser or light emitting transistor structure with a GeSiSn QW or QDactive region in a GaAs P-type base/barrier material 3400.

FIG. 35 shows a possible cross-sectional device depiction of an NPN edgeemitting transistor laser or light emitting transistor (LET) structurewith a GeSiSn QW or QD active region in a GaAs P-type base/barriermaterial 3500.

FIG. 36 shows an exemplary flat band energy diagram of a SCH laserutilizing a GeSn QW or QD, or GeSiSn QW or QD active region located inUID GeSiSn barrier/OCL region with GaAs cladding.

FIG. 37 shows a cross-sectional device depiction of a SCH laserutilizing a GeSn QW or QD region; or GeSiSn QW or QD active regionlocated in UID GeSiSn barrier/OCL region with GaAs cladding.

FIG. 38 shows an exemplary flat band energy diagram of an SCH diodelaser utilizing a GeSn QW or QD, or GeSiSn QW or QD region located inGaAs barrier/OCL region with type InGaP cladding.

FIG. 39 shows a planar growth of strained GeSn (low Sn %) or GeSiSn (lowSi % and low Sn %) on GeSiSn, with GeSiSn barriers above and below a QWGeSn film.

FIG. 40 shows an island growth of strained GeSn (high Sn %) on GeSiSnbarrier layer with a subsequent formation of a QD layer.

FIG. 41 shows an exemplary flat band energy diagram of an NPN HBT withan ordered InGaP emitter, GeSiSn base, GaAs collector.

FIG. 42 shows an exemplary flat band energy diagram of an NPN HBT withan ordered InGaP N emitter, where the base is compositionally gradedGeSiSn—GeSn. The compositionally graded GeSiSn—GeSn base layer cancomprise at the emitter-base interface may be lattice matched or nearlatticed or strained Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAs, where theGeSiSn may be compositionally graded by reducing the Si content andincreasing Ge content to GeSn at the collector interface. The gradingrange can go from GeSiSn at the emitter-base junction to GeSn at thebase-collector junction at various compositions.

FIG. 43 shows an exemplary flat band energy diagram of an inverted NPNHBT structure where an emitter is grown first, a base material iscoherently strained GeSiSn, a collector up structure.

FIG. 44 shows an exemplary flat band energy diagram of an inverted NPNHBT structure where an emitter is grown first, a base material iscoherently strained GeSi, a collector up structure.

FIG. 45 shows an exemplary flat band energy diagram of an NPNconfiguration where a compressively strained GeSiSn HBT collector grownfirst, emitter up.

FIG. 46 shows an exemplary flat band energy diagram of a GeSiSn DoubleHBT Structure graded Emitter and graded Collector grown first, where aGeSiSn base can be compressively strained.

FIG. 47 shows an exemplary flat band energy diagram of an NPN AlGaAsemitter-GeSiSn base-GaAs collector double HBT.

FIG. 48 shows an exemplary flat band energy diagram of an NPN HBT laserwith AlGaAs emitter/cladding and AlGaAs collector/cladding utilizing aGeSn QW or QD, or GeSiSn QW or QD region with GaAs barrier/OCL regionfor use as a transistor laser or light emitting transistor (LET)

FIG. 49 shows a possible exemplary flat band energy band diagram for asymmetric double heterojunction GeSiSn emitter-Ge base-GeSiSn collectorstructure which can work as an NPN or PNP transistor device. The basecould be also GeSi or GeSn or GeSiSn at low Sn %.

FIG. 50 shows a possible exemplary flat band energy band diagram forGeSiSn emitter-graded GeSiSn—GeSn base-GeSiSn collector structure doubleHBT 5000 which can work as an NPN or PNP transistor device. Thecompositionally graded GeSiSn—GeSn base layer can comprise at theemitter-base interface a lattice matched or near latticed matched orcoherently strained Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAs, where theGeSiSn may be compositionally graded by reducing the Si content andincreasing Ge content to GeSn at the collector interface. The gradingrange can go from GeSiSn at the emitter-base junction to GeSn at thebase-collector junction at various compositions.

FIG. 51 shows a possible exemplary flat band energy band diagram for asymmetric double HBT where a Ge QW or QD, or GeSn QW or QD is embeddedin a GeSiSn base region with SiGe emitter/cladding and SiGecollector/cladding.

FIG. 52 shows a possible exemplary flat band energy band diagram for aSi emitter-SiGe base with GeSi QD-Si collector light emitting HBT. Thebase could also be a different composition of GeSi with a higher Sicontent then the QD.

FIG. 53 shows a possible depiction of a cross-sectional device of a Sibased edge emitting transistor laser or light emitting structure,utilizing a GeSiSn quantum well (QW) or quantum (QD) active region. Theactive region could be a GeSi quantum well or quantum dot layer.

FIG. 54 shows a variation of the laser structure of FIG. 52 using SiGecladding layer instead of Si cladding material.

FIG. 55 shows an exemplary flat band energy diagram of a SCH laserutilizing a Ge QW or QD active region located in UIDGe_(1-x)(Si_(0.8)Sn_(0.2))_(z) barrier/OCL. The active region could beGeSiSn, GeSn or GeSi.

FIG. 56 shows energy bandgaps of various semiconductors vs. theirlattice constant. The dotted line encloses the possible GeSiSn materialcompositions.

FIG. 57 shows an exemplary wafer bonding process that enables monolithicjoining of two dissimilar semiconductor materials.

FIG. 58 shows an example of an exemplary flat band energy diagram of awafer bonded NPN GaAs—Ge_(0.95)Si_(0.04)Sn_(0.01)—GaN HBT.

FIG. 58A shows an example of an exemplary flat band energy diagram of awafer bonded NPN GaAs—Ge_(0.98)Si_(0.02)—GaN HBT.

FIG. 59 shows an exemplary flat band energy diagram of an NPN HBTGaAs-graded GeSiSn—GeSn—GaN HBT. The compositionally graded GeSiSn—GeSnbase layer can comprise at the emitter-base interface may be latticematched or near latticed matched or strainedGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAs, where the GeSiSn may becompositionally graded by reducing the Si content and increasing Gecontent to GeSn at the collector interface. The grading range can gofrom GeSiSn at the emitter-base junction to GeSn at the base-collectorjunction at various compositions.

FIG. 60 shows an exemplary cross-sectional device depiction of a waferbonded GaAs—GeSiSn—GaN/SiC NPN double HBT in a mesa configuration.

FIG. 61 shows a possible exemplary cross-section embodiment of a waferbonded GaAs—GeSiSn—GaN/Si NPN double HBT in a mesa configuration.

FIG. 62 shows QuantTera's wafer bonder configuration.

FIG. 63 shows a current-voltage characteristic of a wafer bonded P GeSnto N⁻ GaN showing PN rectifying behavior.

FIG. 64 shows an exemplary flat band energy band diagram of an NPN InGaPemitter-GeSiSn base-GaN collector double HBT.

FIG. 65 shows an exemplary flat band energy diagram of an NPNInGaP-graded Ge—GeSn—GaN HBT. The compositionally graded GeSiSn—GeSnbase layer can comprise at the emitter-base interface may be latticematched or near latticed matched or coherently strainedGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAs. The GeSiSn compositionallygraded by reducing the Si content and increasing Ge content to GeSn atthe collector interface. The grading range can go from GeSiSn at theemitter-base junction to GeSn at the base-collector junction at variouscompositions.

FIG. 66 shows a schematic methodology of the epitaxial lift off (ELO)process.

FIG. 67 a shows a schematic of the top half of an HBT InGaPemitter/GeSiSn base stack with the inclusion of an AlAs separation layerand the GaN collector structure.

FIG. 68 shows a pre-processed top half of an HBT with GeSiSn base regionand the HF etch of the AIAS and ELO.

FIG. 69 shows where a top half of an HBT with GeSiSn base wafer bondedto GaN collector structure.

FIG. 70 shows an inverted top half of an HBT with GeSiSn base region.

FIG. 71 shows the wafer bonding of an inverted top half of an HBT withGeSiSn base region to a GaN collector structure.

FIG. 72 shows a cross-sectional device depiction of a wafer bonded HBTstructure, where the GeSiSn base region is wafer bonded to the GaNcollector.

FIG. 73 shows an exemplary flat band energy diagram of an NPN GaAsemitter-GeSiSn base-wurtzite GaN collector.

FIG. 74 shows an exemplary flat band energy diagram of an NPN GaAsemitter-GeSi base-cubic GaN collector.

FIG. 75 shows various bandgap energies of semiconductor materials as afunction of lattice constant.

FIG. 76 shows a graph of collector current density J_(C) vs.base-emitter voltages (V_(BE)) of different heterojunction bipolartransistor technologies.

FIG. 77 shows an exemplary flat band energy diagram of an NPN GaAsemitter-GeSiSn base-4H SiC collector.

FIG. 78 shows an exemplary flat band energy diagram of an NPN GaAsemitter-GeSi base-4H SiC collector.

FIG. 79 shows an exemplary flat band energy diagram of an NPN GaAsemitter-GeSiSn base-3C SiC collector.

FIG. 80 shows an exemplary flat band energy diagram of an NPN GaAsemitter-graded GeSiSn to GeSn base-4H SiC collector. The compositionallygraded GeSiSn—GeSn base layer can comprise at the emitter-base interfacemay be lattice matched or near latticed matched or coherently strainedGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAs, where the GeSiSn may becompositionally graded by reducing the Si content and increasing Gecontent to GeSn at the collector interface. The grading range can gofrom GeSiSn at the emitter-base junction to GeSn at the base-collectorjunction at various compositions.

FIG. 81 shows an exemplary flat band energy diagram of an NPN GaAsemitter-GeSiSn base-ZnSe collector.

FIG. 82 shows an exemplary schematic embodiment of an NPNGaAs—GeSiSn—ZnSe double heterojunction bipolar transistor in a mesaconfiguration.

FIG. 83 shows an exemplary flat band energy diagram of an NPN GaAsemitter-graded GeSiSn to GeSn base-ZnSe collector HBT. Thecompositionally graded GeSiSn—GeSn base layer can comprise at theemitter-base interface may be lattice matched or near latticed matchedor strained Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAs, where the GeSiSn maybe compositionally graded by reducing the Si content and increasing Gecontent to GeSn at the collector interface. The grading range can gofrom GeSiSn at the emitter-base junction to GeSn at the base-collectorjunction at various compositions.

FIG. 84 shows an exemplary flat band energy diagram of a separateconfinement heterostructure (SCH) laser utilizing a GeSn QW or QD regionlocated in UID GeSiSn barrier/OCL region with SiGe cladding layers.

FIG. 85 shows an exemplary flat band energy diagram of a transistorlaser or LET structure Si emitter-GeSiSn base/barrier with GeSn QW orQD-SiGe collector.

FIG. 86 shows a possible exemplary schematic embodiment of a Si basededge emitting transistor laser or light emitting structure in a mesaconfiguration. The active region can utilize a GeSiSn QW or QD at low Sn%.

FIG. 87 shows a possible exemplary method of using pulsed laserdeposition (PLD) deposited GeSn on GeSiSn and InAlN on GaN to promoteadhesion and enhance heterojunction electrical characteristics for waferbonding. Other compatible materials to promote adhesion and electricalcharacteristics may be InGaN or InN or AlN or AlGaN to the GaN surfacefor better wafer bonding.

FIG. 88 shows the exemplary flat band energy band diagram showing theenergy band alignments of NPN InGaP Emitter-GaAs Base-GaN Collector HBT.

FIG. 89 shows a possible exemplary cross-section device depiction of thewafer bonded InGaP—GaAs—GaN NPN HBT 8920 in a mesa configuration.

For simplicity and clarity of illustration, the drawing figuresillustrate the general manner of construction, and descriptions anddetails of well-known features and techniques may be omitted to avoidunnecessarily obscuring the present disclosure. Elements in the drawingfigures are not necessarily drawn to scale. For example, the dimensionsof some of the elements in the figures may be exaggerated relative toother elements to help improve understanding of embodiments of thepresent disclosure. The same reference numerals in different figuresdenote the same elements.

The terms “first,” “second,” “third,” “fourth,” and the like in thedescription and in the claims, if any, are used for distinguishingbetween similar elements and not necessarily for describing a particularhierarchical, sequential, or chronological order. It is to be understoodthat the terms so used are interchangeable under appropriatecircumstances such that the embodiments described herein are, forexample, capable of operation in sequences other than those illustratedor otherwise described herein. Furthermore, the terms “include,” and“have,” and any variations thereof, are intended to cover anon-exclusive inclusion, such that a process, method, system, article,device, or apparatus that comprises a list of elements is notnecessarily limited to those elements, but may include other elementsnot expressly listed or inherent to such process, method, system,article, device, or apparatus.

The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,”“under,” and the like in the description and in the claims, if any, areused for descriptive purposes and not necessarily for describingpermanent relative positions. It is to be understood that the terms soused are interchangeable under appropriate circumstances such that theembodiments described herein are, for example, capable of operation inother orientations than those illustrated or otherwise described herein.

The terms “couple,” “coupled,” “couples,” “coupling,” and the likeshould be broadly understood and refer to connecting two or moreelements or signals, electrically, mechanically or otherwise. Two ormore electrical elements may be electrically coupled, but notmechanically or otherwise coupled; two or more mechanical elements maybe mechanically coupled, but not electrically or otherwise coupled; twoor more electrical elements may be mechanically coupled, but notelectrically or otherwise coupled. Coupling (whether mechanical,electrical, or otherwise) may be for any length of time, e.g., permanentor semi-permanent or only for an instant.

“Electrical coupling” and the like should be broadly understood andinclude coupling involving any electrical signal, whether a powersignal, a data signal, and/or other types or combinations of electricalsignals. “Mechanical coupling” and the like should be broadly understoodand include mechanical coupling of all types. The absence of the word“removably,” “removable,” and the like near the word “coupled,” and thelike does not mean that the coupling, etc. in question is or is notremovable.

DETAILED DESCRIPTION

The fabrication of a germanium-silicon-tin (Ge_(1-x-y)Si_(x)Sn_(y))semiconductor may be useful as a semiconductor material of aheterojunction bipolar transistor and/or light emitting transistor ortransistor laser or light emitting device or laser or light absorbing orphoto-diode or photo-transistor for electronics and photonics isdescribed herein. Where Ge_(1-x-y)Si_(x)Sn_(y) may be used as the basematerial in a heterojunction transistor; or can be used as the activeregion of a light emitting transistor or transistor laser or lightemitting device or laser; or in a photo-diode or photo-transistor isdescribed. In one embodiment, a method of manufacturing a heterojunctionbipolar transistor includes forming a Ge_(1-x-y)Si_(x)Sn_(y) baseregion. Note that Ge_(1-x-y)Si_(x)Sn_(y) may at various compositions belattice matched to the lattice constants of GaAs and Ge semiconductors.Here y can vary from 0≤y≤0.1, and x can vary 0<x≤0.4.Ge_(1-x-y)Si_(x)Sn_(y) can be comprised materials of Ge, Ge_(1-a)Si_(a),Ge_(1-b)Sn_(b), and Si_(1-c)Sn_(c) at various compositions which mayalso be latticed matched or near latticed matched or strained to GaAs orGe. GeSiSn may be also written in the following formGe_(1-z)(Si_(1-k)Sn_(k))_(z). Where the value of k may be equal to 0.2or near that value and have a range of values 0.1≤k≤0.4 and where z hasa range of 0<z≤0.5. However for the GeSiSn latticed matched orcoherently strained to GaAs or Ge there may be a range of values that kcan have, which may be close to 0.2. One may then write GeSiSn latticedmatched or near latticed matched or strained to GaAs or Ge asGe_(1-z)(Si_(0.8)Sn_(0.2))_(z). In this designation the subscripts underthe Si_(0.8) and Sn_(0.2) may be empirical values and can have a degreeof variation as given by 0.1≤k≤0.4 in Ge_(1-z)(Si_(1-k)Sn_(k))_(z). Thisform may be useful for the following materials compositionGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) where z is 0<z≤0.5, which may result inthat Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) may be lattice matched or nearlatticed matched or pseudomorphic to Ge or GaAs semiconductors. ThusGeSiSn has a range of Si and Sn for the lattice matched condition toGaAs and Ge. Here the lattice constant of GaAs and Ge may be about 5.65Å. The lattice mismatch between Ge and GaAs may be less than about 0.1%which may be considered near-latticed matched or lattice matched. AlsoGeSiSn when grown on GaAs or Ge may be tensile or compressivelystrained, which may be useful in devices. Sometimes for strained GeSiSnthe term pseudomorphic may be used. GeSi designated by Ge_(1-a)Si_(a)may also be latticed matched or near lattice matched or coherentlystrained to GaAs or Ge. Here the value of a may be about 0.02, with arange of variation of 0.0<a≤0.03. Thus the designation forGe_(0.98)Si_(0.02) may represent GeSi lattice matched or near latticedmatched or coherently strained to GaAs or Ge. In this designation thesubscripts under the Ge_(0.98) and Si_(0.02) may be empirical values andcan have a degree of variation as given by 0.0<a≤0.3 in Ge_(1-a)Si_(a).The materials of Ge, Ge_(1-a)Si_(a), Ge_(1-b)Sn_(b), and Si_(1-c)Sn_(c)may be interchanged with Ge_(1-x-y)Si_(x)Sn_(y) materials system for avariation of the embodiments of the devices elucidated. It should benoted where the subscripts are missing GeSiSn refers toGe_(1-x-y)Si_(x)Sn_(y), GeSi refers to Ge_(1-a)Si_(a), GeSn refers toGe_(1-b)Sn_(b), and SiSn refers to Si_(1-c)Sn_(c). This terminologyrefers to the fact that alloy semiconductor GeSiSn consists of thefollowing component materials GeSi, GeSn and SiSn at various possiblecompositions. Also it should be noted for GeSiSn where the Sn content iszero that GeSi can be grown latticed or near latticed matched to GaAsand Ge. This value may be close to the composition Ge_(0.98)Si_(0.02).Throughout the context of the document Ge_(1-x-y)Si_(x)Sn_(y) may bereferred to as GeSiSn where y can vary from 0≤y≤0.1, and x can vary0<x≤0.4. Also the term graded or grading refers to compositional gradingof the semiconductor alloy.

In a further embodiment, a device includes: a first heterojunctionbipolar transistor comprising a PNP device having a first GeSiSn base;and a second heterojunction bipolar transistor comprising an NPN devicehaving a second GeSiSn base, wherein the first and second heterojunctionbipolar transistors are located over a common substrate. In anotherembodiment, method of manufacturing a device includes: forming a firstheterojunction bipolar transistor comprising a PNP device having a firstGeSiSn base; and forming a second heterojunction bipolar transistorcomprising an NPN device having a second GeSiSn base, wherein formingthe first and second heterojunction bipolar transistors occursimultaneously with each other over a common substrate. In yet anotherembodiment, a device includes: a first bipolar transistor comprising afirst GeSiSn base; and a second bipolar transistor comprising a secondGeSiSn base, wherein the first and second bipolar transistors arecomplementary devices and are located over a common substrate. In afurther embodiment, a method of manufacturing a device includes: forminga first bipolar transistor comprising a first GeSiSn base; and forming asecond bipolar transistor comprising a second GeSiSn base, whereinforming the first and second bipolar transistors occur simultaneouslywith each other over a common substrate. In still another embodiment, abipolar transistor includes a GeSiSn base region, and in yet anotherembodiment, a method of manufacturing a bipolar transistor includesproviding a GeSiSn base region. In a further embodiment, a transistorlaser or light emitting transistor includes a GeSiSn active region, andin another embodiment, a method of forming a transistor laser includesforming a GeSiSn active region. The description herein elucidates amethodology for making a heterojunction bipolar transistor (HBT) thatutilizes GeSiSn as the base material. Furthermore, the unique propertiesof GeSiSn can be utilized as the active region of a variation of thetransistor which is the transistor laser, or in a light emitting devicelike a laser. The GeSiSn can be used also as a light detection materialfor photo-diodes or photo-transistors embodiments described herein canrelate to the following: GeSn which has the smallest bandgap energy forthe material systems GeSi, GaN, GaAs, Si, InP, Ge, Sn, AlAs, InAs, GaP,ZnSe, SiC and the alloy semiconductor GaNInAs etc., and thus would beuseful for making a heterojunction bipolar transistor, laser ortransistor laser device or light emitting transistor or photo-diode orphoto-transistor. Embodiments described herein can relate to GeSiSn(Ge_(1-x-y)Si_(x)Sn_(y)) or GeSi (Ge_(1-a)Si_(a)) or GeSn(Ge_(1-b)Sn_(b)) or SiSn (Si_(1-c)Sn_(c)), and may have small bandgapenergies (less than 1 eV), and may be relaxed, lattice matched, nearlattice matched, pseudomorphic, tensile strained or compressivelystrained or coherently strained. Note that besides GeSiSn, that Ge orGeSn or GeSi or SiSn may make useful base materials for a heterojunctionbipolar transistor (HBT). Nomenclature: Ga (gallium), N (nitrogen ornitride), As (arsenic or arsenide), Si (silicon), In (indium), P(phosphorous or phosphide), Ge (germanium), Al (aluminum), Sn (tin), Sb(antimony or antimonide), B (boron), C (carbon, carbide), Zn (zinc), andSe (selenium, selenide), Te (tellurium or telluride).

The embodiments can relate to the following:

-   -   1) Bipolar transistor using a latticed matched GeSiSn or        strained GeSiSn base.    -   2) Bipolar transistor using a latticed matched GeSn or strained        GeSn base.    -   3) Bipolar transistor using a latticed matched SiSn or strained        SiSn base.    -   4) Bipolar transistor using a latticed matched GeSi or strained        GeSi base.    -   5) Bipolar transistor using a compositionally graded GeSiSn—GeSn        base.    -   6) Bipolar light emitting transistor or transistor laser using        in the base region a strained GeSiSn quantum well, quantum dot,        or GeSn quantum well (QW), quantum wire, or quantum dot (QD)        active region.    -   7) Light emitting or laser structure using GeSiSn or strained Ge        quantum well (QW), quantum wire, or quantum dot (QD) active        region.    -   8) A photo-diode using a GeSiSn absorbing region.    -   9) A photo-transistor using a GeSiSn absorbing region.        The same or different embodiments can relate to:    -   1) Lateral structures (edge emitting).    -   2) Vertical structures.    -   3) Inverted vertical structures.    -   4) Indirect bandgap GeSiSn.    -   5) Indirect bandgap SiSn.    -   6) Indirect bandgap GeSi.    -   7) Indirect bandgap GeSn    -   10) Direct bandgap GeSn.    -   11) Strained GeSiSn: tensile or compressively strained.    -   12) Single or Multiple quantum well layers.    -   13) Single or Multiple quantum dot layers.    -   14) Single or Multiple quantum wire layers.

In one embodiment, a heterojunction bipolar transistor can include aGeSiSn base region. In another embodiment, a heterojunction bipolartransistor can include a GeSn base region. In another embodiment, aheterojunction bipolar transistor can include a Ge base region. Inanother embodiment, a heterojunction bipolar transistor can include aGeSi base region. In another embodiment, a heterojunction bipolartransistor can include a SiSn base region. In another embodiment, amethod of manufacturing a heterojunction bipolar transistor can includeforming a GeSiSn base region. Note that the term GeSiSn may be comprisedof the following materials Ge, GeSi, GeSn, or SiSn. In a furtherembodiment, a device can include a first heterojunction bipolartransistor comprising a PNP device having a first GeSiSn base, and asecond heterojunction bipolar transistor including an NPN device havinga second GeSiSn base.

A bipolar transistor or bipolar junction transistor is a three terminalor three layer device that relies on doping (adding “impurity” atoms) ofthe semiconductor layers to form N-type or “N” (electron surplus layer)semiconductor and P-type or “P” (electron deficient layer) semiconductorto form PN junction (diodes) in a three terminal configuration. Thisthree terminal or three layer device can include back-to-back PNjunctions to form a three layer sandwich with each of the layers namedthe emitter, base, and collector. There are two kinds of bipolartransistors, NPN and PNP.

For simplicity and clarity of illustration, the drawing figuresillustrate the general manner of construction, and descriptions anddetails of well-known features and techniques may be omitted to avoidunnecessarily obscuring the present disclosure. Elements in the drawingfigures are not necessarily drawn to scale. For example, the dimensionsof some of the elements in the figures may be exaggerated relative toother elements to help improve understanding of embodiments of thepresent disclosure. The same reference numerals in different figuresdenote the same elements.

FIG. 1 shows a general configuration of a bipolar transistor as a threeterminal device in its two constituent forms NPN 0101 and PNP 0108. TheNPN 0101 structure comprises an N-type emitter 0102, connected to aP-type base 0103, which is then connected to a N-type collector 0104region, which comprises the three terminal device. The correspondingcurrents in the three terminal device correspond to the emitter currentI_(E) 0105, base current I_(B) 0106, and collector current I_(C) 0107.The NPN 0101 device has a junction at the emitter-base, where theapplied voltage is V_(BE) 0115, and a second junction at thebase-collector, where the applied voltage is V_(BC) 0116.

The PNP 0108 structure comprises a P-type emitter 0109, connected to anN-type base 0110, which is then connected to a P-type collector 0111region, which comprises the three terminal device. The correspondingcurrents in the three terminal device correspond to the emitter currentI_(E) 0112, base current I_(B) 0113, and collector current I_(C) 0114.The PNP 0108 device has a junction at the emitter-base, where theapplied voltage is V_(BE) 0117, and a second junction is at thebase-collector, where the applied voltage is V_(BC) 0118. Thebase-emitter voltage V_(BE) turns on the transistor and generally isoperated in forward bias, and the base-collector voltage V_(BC) isgenerally reversed biased and also determines the breakdown voltage ofthe device.

The base region controls the operation of the transistor. Thecharacteristics and properties of the base material and the base-emitterjunction and the base-collector junction are the dominant factors thatdetermine the electronic properties of bipolar and heterojunctionbipolar transistors. Thus the utilization of a new type of base materialin these transistors allows for the development of vastly improvedtransistors for high speed and power efficient operation.

Semiconductors can be discussed in terms of their energy band structure.The energy band structure shows the allowable carrier (electron or hole)energy states for semiconductor as a function of the crystal momentumdirection. The energy band structure can be divided into two mainregions: the conduction band; and the valence band. N-type materialconduction relies on free movement of electrons in the conduction bandof the material. The conduction band can be characterized by theconduction band energy level (lowest energy in the conduction band).P-type material conduction relies on the free movement of holes (hole:absence of an electron) in the valence band of the material. The valenceband is characterized by the valence band energy level (or the highestenergy level in the valence band). The difference between the conductionband energy level and the valence band energy level determine the energybandgap of the semiconductor (difference of the conduction band energyminima to the valence band energy maxima).

At the PN junctions of the bipolar transistor, there exists a depletionzone that in the absence of an externally applied electric fieldprevents the movement of the charge carriers across the junctions ordifferent layers. The operation of this device relies on two types ofcarriers, free electrons (negative charges in the conduction band) andfree holes (absent electron charge carrier, positive charge in thevalence band). Thus, the name bipolar is ascribed to this device becauseits operation involves both electrons and holes, as opposed to unipolardevices like field effect transistors whose operation involves only oneof electrons or holes.

The bipolar transistor has three distinct regions: the emitter, thebase, and the collector. The flow of charges (called electrical currentor current) in this transistor is due to the bidirectional diffusion ofcharge carriers across the junction. The bipolar transistor is biased asfollows. The emitter is forward biased via the contact pads with thevoltage potential (base-emitter voltage V_(BE)) to force charge carriersfrom the emitter to the base. The collector is reversed biased via thecontact pads with a voltage potential (base-collector voltage) thatcauses charge carriers to be attracted from the base to the collector.The corresponding currents are called the emitter current, base current,and the collector current.

FIG. 2 shows a general configuration of a bipolar transistor as avertical stack geometry. Typically the structure can be grownepitaxially, ion implanted or fabricated by various means. For avertical bipolar transistor, typically a conducting or insulatingsubstrate 0201 is used as the seed crystal to start the growth of thestructure. A highly conducting sub-collector 0202 is then grown,followed by a low doped collector 0203. The base 0204 which is ofopposite conductivity as the collector 0203 is then grown, followed byan emitter 0205, and finally a highly conducting contact layer 0206.Electrical contact is made to device via the metalized contact pads:emitter contact 0207, base contact 0208, and collector contact 0209. Thevoltages and currents are applied to the device via the contact pads.Vertical configuration offers some advantages.

Some of the advantages of a bipolar device are: typically in an NPNconfiguration electrons travel vertically in the device from the emitterto the collector. Thus it is straightforward to produce devices wherethe electron transit time through the device is short (high cut offfrequency F_(t)). Generally the entire area of the emitter contactconducts the current; thus one can have high current densities in asmall area, thus allowing for high circuit densities. The turn-onvoltage (voltage across the base-emitter junction) V_(BE) is independentof device processing issues like size because it corresponds to thepotential at the base-emitter junction, thus process variations across awafer can be minimized which is desirable for manufacturing. The turn-onvoltage V_(BE) controls the output current at the collector I_(C) andresults in a high transconductance g_(m)=eI_(C)/k_(B)T, where “e” is thecharge of the electron, “I_(C)” is the collector current, “k_(B)” isBoltzmann's constant, and “T” is the temperature. This is the highesttransconductance available for any three terminal device and allowscircuit operation with low V_(BE) swings.

The operation of the bipolar transistor (transistor action) is based onthe flow of charge carriers injected from the emitter into the basewhich can diffuse into the collector forming the emitter to collectorcurrent (collector current). The free charge carriers initially in theemitter are called majority carriers. The majority charge carriers thatare injected into the base from the emitter, once in the base, arecalled minority carriers, which then can diffuse to the collector. Thebase region controls the flow of the minority carriers injected into thebase thus controlling the flow of the collector current from the emitterto the collector. By drawing out the minority carriers that are injectedinto the base from the emitter, small levels of minority carriers drawnfrom the base control the larger collector current that flows from theemitter to the collector. Also, the base region is made thin to enhancethe diffusion of carriers from the emitter to the collector.

The current gain or “beta” of the bipolar transistor is the ratio of thecollector current I_(C) to the base current I_(B). Basically, the ratiois the number of carriers that get across the transistor from theemitter to the collector, vs. the number of carriers that get caught inthe base.

For a typical NPN transistor, the biasing scheme is as such. The emitterto base V_(BE) bias is such that the base is biased slightly positive ascompared to the emitter. The collector to base V_(BC) bias is such thatthe collector is biased much more positively than the base. This biasingscheme can ensure that, for small values of base current, large valuesof collector currents can be controlled. The current gain is typicallyabout “100”.

For a typical PNP transistor, the biasing scheme is as such. The emitterto base V_(BE) bias is such that the base is biased slightly negative ascompared to the emitter. The collector to base V_(BC) bias is such thatthe collector is biased much more negatively than the base. This biasingscheme can ensure that, for small values of base current, large valuesof collector currents can be controlled.

The bipolar homojunction transistor can be made of one semiconductormaterial. The bipolar transistor can be used as a switch, amplifier, oroscillator, etc. It can be fabricated in discrete (single) component oras a component in integrated circuits.

Heterojunction bipolar junction transistors (HBT) can differ from thebipolar transistor (also called a homojunction bipolar transistor) byusing at least two different semiconductors. The heterojunction bipolartransistor typically uses different semiconductor materials for at leastone of the junctions, the emitter-base junction, and/or thebase-collector junction. The use of differing semiconductor materials iscalled a heterojunction.

Heterojunction bipolar transistors (HBTs) can be advantageous in somesituations for formation of the emitter-base junction. In homojunctiontransistors, the emitter is typically doped (impurity incorporation withan atomic element to create free charge carriers) more heavily than thebase region. If the heterojunction is designed properly, the emitter hasan energy bandgap greater than the base region. If the conduction andvalence band alignment of the two materials that form the heterojunctionis proper, it is then possible to limit the injection of majoritycarriers (initial free charge carriers in the base) of the base regioninto the emitter region (or can be termed as to limit the minoritycarrier injection into the emitter). This occurs because theheterojunction can create a potential barrier either in the valence orconduction band to block the majority carriers in the base, thuseliminating injection of majority carriers from the base into theemitter. In the heterojunction transistor, the base can be heavily dopedat concentrations much greater than the emitter material. The physics ofthe heterojunction can be strongly determined by the conduction andvalence band alignment between the materials.

FIG. 3 shows a flat band energy diagram for three typical heterojunctionsituations between emitter and base materials (focuses on the case wherewe have an N-type emitter material and a P-type base material): type I,type II, and near zero conduction band offset. The heterojunction is atthe interface between the emitter material and the base material. Thetype of diagram depicted is called a flat band energy diagram, whichrepresents how the conduction band edge 0310 and the valence band edge0311 change as one goes through the dissimilar semiconductor materials.The vertical axis 0312 has the value of Energy with typical units of“eV”, and the horizontal axis 0313 is the relative Distance in arbitraryunits “A.U.” through the heterojunction of semiconductor materials. Theenergy level line called the conduction band edge 0310 is the minimumenergy value of the conduction band, and the energy level line calledthe valence band edge 0311 is the maximum value of the valence band. Thediagram shows distance on the horizontal scale and that is a relativedistance into the semiconductor device. One could put units ofthickness, but that is usually omitted, and this represents a schematicfor carrier transport. The difference between the conduction band edge0310 and the valence band edge 0311 in the base material is the bandgapenergy of the base material. The difference between the conduction bandedge 0310 and the valence band edge 0311 in the emitter material is thebandgap energy of the emitter material.

There are various types of heterojunctions between the emitter and basematerials: (1) Type I heterojunction 0301; (2) Type II heterojunction0302; and (3) near zero conduction band offset 0303 (there can also be anear zero valence band offset) at the heterojunction. Type Iheterojunction has an energy discontinuity at the conduction band andvalence band, where the smaller bandgap at base material 0305 liesbetween the conduction and valence band edges of emitter material 0304.ΔE_(C) is called the conduction band offset at the emitter-baseheterojunction (difference between the conduction band edges in therespective materials), and ΔE_(V) is called the valence band offset atthe emitter-base junction (difference between the valence band edges inthe respective materials). Type II heterojunctions have a discontinuityat the conduction and valence band edge, but the base energy alignmentis staggered or offset. The energy bandgap of base material 0307 can bestaggered above emitter material 0306, and the bandgap as depicted inthe figure (or staggered below the emitter material 0306 bandgap). Onecan have a situation of a zero or near zero conduction band offsetheterojunction 0303 as shown in the figure, where the conduction bandoffset ΔE_(C) is zero or small, typically less than 0.1 eV betweenemitter material 0308 and base material 0309.

For NPN heterojunction transistors, where the emitter material is N-typeand the base material is P-type, a large valence band offset ΔE_(V)between the emitter and the base is desired, as shown in the threecases: (1) Type I heterojunction 0301; (2) Type II heterojunction 0302;and (3) near zero conduction band offset heterojunction 0303. This largevalence band offset ΔE_(V) prevents the back injection of holes from thebase to emitter, which can reduce the gain of the transistor. Thus thebase material bandgap energy should be less than the emitter materialbandgap energy. Looking at the FIG. 3 diagram, it seems that a type IIheterojunction current 0302 would be preferable because it has thelargest valence band offset ΔE_(V), but in some examples, the desiredsituation for the efficient transport of carriers across the base topromote transistor action may be that there is a near zero conductionband offset heterojunction 0303 situation or where the conduction bandoffset ΔE_(C) may be typically less than 0.1 eV.

FIG. 4 shows a flat band energy diagram for three typical heterojunctionsituations between the base material and the collector material (focuseson the case where we have a P-type base material and an N-type collectormaterial): type I, type II, and near zero conduction band offset. Theheterojunction is at the interface between the base material andcollector material. The type of diagram depicted is called a flat bandedge energy diagram, where the vertical axis is the Energy (eV) 0412value and the horizontal axis is a relative Distance (A.U.) 0413 throughheterojunction of semiconductor materials. The energy level lines arecalled the conduction band edge 0410, is the minimum energy value of theconduction band and the valence band edge 0411 is the maximum value ofthe valence band. The diagram shows distance on the horizontal scale,and the distance is a relative distance into the semiconductor device.One could put units of thickness, but that is usually omitted and thisrepresents a schematic for carrier transport. The difference between theconduction band edge 0410 and the valence band edge 0411 in the basematerial is the bandgap energy of the base material. The differencebetween the conduction band edge 0410 and the valence band edge 0411 inthe collector material is the bandgap energy of the collector material.

There are various types of heterojunctions between the base andcollector materials: (1) Type I heterojunction 0401; (2) Type IIheterojunction 0402; and (3) near zero conduction band offset 0403(there can also be a near zero valence band offset) at theheterojunction. Type I heterojunction has an energy discontinuity at theconduction band and valence band, where the smaller bandgap basematerial 0404 regions lies between the conduction and valence band edgesof the collector material 0405. ΔE_(C) is called the conduction bandoffset at the base-collector heterojunction (difference between theconduction band edges in the respective materials), and ΔE_(V) is calledthe valence band offset at the base-collector heterojunction (differencebetween the valence band edges in the respective materials). Type IIheterojunctions have a discontinuity at the conduction and valence bandedge, but the base energy alignment is staggered or offset. The energybandgap of base material 0406 can be staggered above the bandgap ofcollector material 0407 as depicted in the figure (or staggered belowthe bandgap of collector material 0407). One can have a situation of azero or near zero conduction band offset heterojunction 0403 as shown inthe figure, where the conduction band offset ΔE_(C) is zero or small,typically less than 0.1 eV between the base material 0408 and thecollector material 0409.

For NPN heterojunction transistors, where the base material is P-typeand the collector material is typically N-type, one would like a largecollector bandgap energy because this allows the NPN transistor to havea big breakdown voltage. Looking at the FIG. 4 diagram, it seems that atype II heterojunction 0402 would be preferable because the basematerial 0406 has higher conduction band energy than the collectormaterial 0407, but in some examples, the possible desired situation forthe efficient transport of carriers across the base to promotetransistor action is the there may be a near zero conduction band offsetheterojunction 0403 situation or where the conduction band offset ΔE_(C)may be less than 0.1 eV.

FIG. 5 shows a flat band energy diagram through an NPN heterojunctionbipolar transistor 0500 for possibly enhanced carrier transport. Thefigure shows the lineup of the conduction band edge 0504 and the valenceband edge 0505 through the NPN heterojunction transistor 0500. There isa zero conduction or near zero conduction band edge offset ΔE_(C) fromthe N emitter material 0501 to the P base material 0502 to the Ncollector 0503. The emitter-base valence band offset is represented byΔE_(VE) and the base-collector valence band offset is ΔE_(VC). Inphysical situations it is desirable to have the smallest conduction bandoffset that is possible from N emitter material 0501 to P-base material0502 to N collector 0503. Here the bandgap energy of N emitter material0501 is larger than the bandgap energy of P base material 0502, wherethere is a large valence band offset E_(VE) between N emitter material0501 to P base material 0502, and the junction is a heterojunction. Thebandgap energy of N collector material 0503 can be less than, equal to,or greater than the bandgap energy of P base material 0502. Generallythe bandgap energy of N collector material 0503 should be equal to, orgreater than the bandgap energy of P base material 0502. The greater thebandgap energy of N collector material 0503 the better the breakdownvoltage of NPN heterojunction bipolar transistor 0500. This is generallydesirable for high power and robust devices. If N collector material0503 is the same material as P base material 0502, there is ahomojunction at the base-collector junction and a heterojunction at theemitter-base junction, and such a device is called a singleheterojunction bipolar transistor device. If N emitter material 0501 andN collector material 0503 are the same, then the device is called asymmetric double heterojunction bipolar transistor device, and such adevice results in a minimum in zero offset voltage in the measurement ofthe collector current vs. the collector-emitter voltage as a function ofthe stepped voltage bias of the base-emitter junction, which isdesirable to improve the power added efficiency of NPN heterojunctionbipolar transistor 0500. For robust and high power, one would like thecollector bandgap energy to be as large as possible. If the emittermaterial, the base material, and the collector material are alldissimilar, the device would be called an asymmetric doubleheterojunction bipolar transistor device.

The NPN heterojunction transistor can promote efficient transport whenthere may be a zero or near zero or the smallest conduction band offsetbetween emitter-base-collector. In an NPN device, the electrons are keycarrier that makes up the collector current, and the base-emitterjunction controls this electron current. The base alignment of theconduction band offset can be desirable in some examples. Largeconduction band energy offsets or discontinuities at the emitter-base orcollector-base junctions can hinder electron transport.

FIG. 6 shows a flat band energy diagram through a PNP heterojunctionbipolar transistor 0600 for possibly enhanced carrier transport. Thefigure shows the line-up of conduction band edge 0604 and valence bandedge 0605 through PNP heterojunction transistor 0600. There is a zerovalence band or near zero valence band edge offset ΔE_(V) from P emittermaterial 0601 to N base material 0602 to P collector 0603. Theemitter-base conduction band offset is represented by ΔE_(CE) and thebase-collector conduction band offset is ΔE_(CC). In physical situationsit is desirable to have the smallest valence band offset that ispossible from P emitter material 0601 to N base material 0602 to Pcollector 0603. Here the bandgap energy of P emitter material 0601 islarger than the bandgap energy of N base material 0602, where there is alarge conduction band offset ΔE_(CE) between P emitter material 0601 toN base material 0602, and the junction is a heterojunction. The bandgapenergy P collector material 0603 can be less than, equal to, or greaterthan the bandgap energy of N base material 0602. Generally the bandgapenergy of P collector material 0603 should be equal to, or greater thanthe bandgap energy of N-base material 0602. The greater the bandgapenergy of P collector material 0603 the better the breakdown voltage ofPNP heterojunction bipolar transistor 0600. This is generally desirablefor high power and robust devices. If P collector material 0603 is thesame material as N base material 0602, there is a homojunction at thebase-collector junction and a heterojunction at the emitter-basejunction, and such a device is called a single heterojunction bipolartransistor device. If P emitter material 0601 and P collector material0603 are the same, then the device is called a symmetric doubleheterojunction bipolar transistor device, and such a device results in aminimum in zero offset voltage in the measurement of the collectorcurrent vs. the collector-emitter voltage as a function of the steppedvoltage bias of the base-emitter junction, which is desirable to improvethe power added efficiency of PNP heterojunction bipolar transistor0600. For robust and high power, one would like the collector bandgapenergy to be as large as possible. If the emitter material, the basematerial, and the collector material are all dissimilar the device wouldbe called an asymmetric double heterojunction bipolar transistor device.

A PNP heterojunction transistor can promote efficient transport whenthere may be a zero or near zero valence band offset betweenemitter-base-collector. In a PNP device, the holes are key carriers thatmake up the collector current, and the base controls this hole current.The base alignment of the valence band offset can be desirable in someexamples. Valence band energy discontinuities at the emitter-base orcollector-base junctions can hinder hole transport.

The relationship of the conduction and valence band offsets for manysemiconductors may be well studied, and numerous values of theconduction band offsets ΔE_(C) and valence band offsets ΔE_(V) betweendissimilar semiconductors (heterojunction) have been published in theliterature.

Unlike homojunction bipolar transistors, heterojunction bipolartransistors (HBTs) allow for a higher base doping density (>1×10¹⁹ cm⁻³)thus reducing the base resistance and maintaining current gain. For NPNHBTs, higher base doping density can occur as a result of the largevalence band offset at the emitter-base junction. For PNP HBTs, higherbase doping density can occur as a result of the large conduction bandoffset at the emitter-base junction.

Typically, one would like to have the highest doping density that ispossible in the base. Typically the highest levels of base doping aregreater than 1×10¹⁹ cm⁻³. High doping levels may be typically greaterthan 1×10¹⁸ cm⁻³ range and typically low doping levels may be in the1×10¹⁶ cm⁻³ to 5×10¹⁷ cm⁻³ range. The high doping density in the basecauses a reduction in the base sheet resistance thus allowing thetransistor to have larger F_(max) (e.g., the maximum frequency to getpower gain out of the transistor). Also, by having high base doping onecan reduce the thickness of the base and increase the F_(t) (e.g., thetransit frequency, time for carrier to go across base region). Therelationship between transit frequency F_(t) and the maximum oscillationfrequency F_(max) is as follows for an HBT:F_(max)=(F_(t)/8πR_(B)C_(CB))^(1/2). The transit frequency F_(t) isbasically inverse of the time for the electron to traverse the emitter,base and collector. The parameters R_(B) and C_(CB) refer to the basesheet resistance and the capacitance of the collector-base junction. Theparameter F_(max) is the unity power gain frequency and indicates themaximum frequency with power gain from a device.

The reason why heterojunction bipolar transistors (HBTs) can beadvantageous is that heterojunction bipolar transistors (HBTs) may allowfor a higher base doping density (>1×10¹⁹ cm⁻³) thus reducing the baseresistance and maintaining current gain. For various choices of theemitter and base materials, it is possible to obtain large valence bandoffset ΔE_(V). This large valence band offset ΔE_(V) prevents the backinjection of minority carriers into the emitter, thus keeping the gainof the HBT high (no degradation of the gain with high doping of the basematerial).

In some examples for the base-collector junction, the base-collectorbreakdown voltage is set by the energy bandgap of the collectormaterial. Typically, one would like to have a low energy bandgap basematerial (typically these are relevant semiconductors with bandgaps lessthan 1.0 eV, like GeSn or Ge or GeSi or GeSiSn or InGaAs or GaAsSbbecause that sets the turn-on voltage of the base-emitter junction orthe onset of transistor action. However, in a homojunction (base andcollector materials are the same), a low energy bandgap at the collectorcan result in a low base-collector breakdown voltage. Thus a largepotential difference between the base and the collector junction couldallow the transistor to have a low breakdown voltage which causes thetransistor to be easily damaged thus hurting ruggedness. In aheterojunction bipolar transistor, it is possible to combine a lowenergy bandgap base region with a large energy bandgap collector regionthus allowing for a large breakdown voltage. Heterojunctions transistorproperties can be enhanced utilizing specific materials for the emitter,base, and collector.

The characteristics and properties of the base and the base-emitterjunction and the base-collector junction are the dominant factors thatdetermine the electronic properties of bipolar and heterojunctionbipolar transistors. Thus the utilization of a new type of base materiallike GeSiSn in these transistors allows for the development of vastlyimproved transistors for high speed and power efficient operation.

GeSiSn is a useful material for use as the base material for bipolartransistors because it can be latticed matched to GaAs or Ge. It canalso be grown pseudomorphic, tensile strained or compressively strainedon GaAs or Ge. GeSiSn can be used a quantum wells (QW) or quantum dots(QD) active region for light emission in devices such as a lightemitter, laser or transistor laser or light emitting transistor (LET).For light emitters or absorbers, GeSiSn can be a barrier of opticalconfinement layer (OCL).

Lasers are devices that can produce intense narrowly divergent,substantially single wavelength (monochromatic), coherent light. Laserlight of different wavelengths can be advantageously applied in manyfields, including biological, medical, military, space, industrial,commercial, computer, wireless devices, and telecommunications.

Semiconductor lasers may utilize an active region, which may be formedwith a homojunction (using similar materials), single or doubleheterojunction (using dissimilar materials), or with a quantum well(“QW”), quantum dot (“QD”), quantum wire, or quantum cascade region. Theenergy transitions can occur from interband or inter-sub-band electronicstates. The quantum well, quantum dot, or quantum wire structure may beformed when a low energy bandgap semiconductor material is typicallysurrounded or confined by a larger bandgap semiconductor materials.These quantum confined heterostructures can be type I, type II, or typeIII (broken energy alignment). The fundamental wavelength thatcharacterizes quantum well (QW) or quantum dot (QD) is determinedprimarily by the thickness, composition, and material of the quantumwell.

In order for lasing to occur, a laser device typically has a resonantcavity and a gain medium to create population inversion. In some highlyefficient semiconductor laser examples, population inversion generallyoccurs with the injection of electrical carriers into the active region,and the resonant cavity is typically formed by a pair of mirrors thatsurround the gain medium. The method of injection of carriers can bedivided into electrical injection of carriers and optical pumping forinjection of carriers. Electrical injection is generally performed by anelectrical current or voltage biasing of the laser and forms the basisof the electrical injection laser. Optical pumping typically usesincident radiation that allows the formation of electrons and holes inthe laser. These methods can be operated in a continuous wave (CW)pulsed, synchronous, or asynchronous modes.

FIG. 7 shows a general configuration of a PN junction laser or injectionlaser diode 0700, with a quantum well or quantum dot 0703 active region.This PN junction device operates on the principle of minority injectionof carriers (electrons and holes, the I_(diode) current) into the activeregion and waveguide 0705. The P⁺ cladding 0701 region may serve as theinjection of holes. N⁺ cladding 0706 may serve as the injection ofelectrons. It can be possible when a low bandgap material is placedinside a larger energy bandgap, like the optical confinement layers OCL0702 and OCL 0704, the formation of QW or QD 0703 can be formed. TheseQW or QD 0703 can serve as the active region for the collection of bothelectrons and holes and produces the inverted population necessary forlaser operation. The wide bandgap P⁺ cladding 0701 and N⁺ cladding 0706semiconductors provide for the optical confinement because their indexof refraction is generally lower than that of the optical confinementmaterials OCL 0702 and OCL 0704. The cladding layers also providefunneling of the electrical carriers to the QW or QD 0703 regions. Light0707 can be produced by recombination of carriers in the QW or QD. Thereare the optical confinement layers (OCL) which serve as the barrier tothe QW or QD region thus providing for the quantum confinement, and alsoserves as the waveguide material. The OCL layers generally have bandgapenergies between that of the QW or QD and the wide bandgap energycladding layers. The combination of the QW or QD 0703 and the OCL 0702and OCL 0704 form the active region and waveguide 0705 of the laserstructure.

FIG. 8 shows an exemplary flat band energy diagram showing theconduction band edge 0808 and the valence band edge 0809 of a separateconfinement heterostructure (SCH) laser 0800 with an active QW or QD0803 region. The OCL1 0802 and OCL2 0804 form the barrier layers to theQW or QD 0803 which allows for quantum confinement and can be of thetype I heterojunction band alignment. Such a structure providesefficient recombination of the carriers and good optical confinement ofthe light produced from the recombination of the carriers. The P⁺cladding large bandgap 0801 and the N⁺ cladding large bandgap 0806provides for minority carrier injection and funnels the carriers intothe waveguide region ultimately recombining in the QW or QD 0803 activeregion. The cladding layers form the boundary for the waveguide 0807with the OCL1 0802 and OCL2 0804 regions thus providing for efficientconfinement of light. In this design the P⁺ cladding large bandgap 0801and N⁺ cladding large bandgap 0806 have the largest bandgap energies inthe device structure. Next the OCL1 and OCL2 layers have the nextlargest bandgap energies. Finally the QW or QD 0803 materials have thesmallest bandgap energies. In this design the P⁺ cladding large bandgap0801 and OCL1 0802 has a type I heterojunction alignment, and in thisdesign the N⁺ cladding large bandgap 0806 and OCL2 0804 also has a typeI heterojunction alignment. Various configuration of the SCH arepossible for enhancement of the laser. Note that though the figure showsonly one QW or QD region, multiple QW or QD regions can be used, ifhigher efficiencies are wanted. Typically such a structure is insertedinto a resonant cavity for the light amplification that is required forlaser operation.

Two common types of semiconductor lasers: (1) in-plane, also known asedge emitting or Fabry Perot lasers (also includes distributed feedbacklasers); and (2) surface emitting also known as vertical cavity surfaceemitting lasers (“VCSELs”). Edge emitting lasers emit light from theedge of the semiconductor wafer whereas VCSELs emits light from thesurface of the laser. For the edge emitter, the resonant cavity istypically formed with cleaved mirrors at each end of the active region.

FIG. 9 is a perspective schematic of a typical edge emitting injectiondiode laser or in-plane semiconductor laser 0901. The edge emittinglaser 0901 can comprise a substrate 0910 with an active region 0906disposed between a P-type cladding layer 0904 and an N-type claddinglayer 0905. Cleaved facets on the front 0908 and on the back 0909 of thelaser typically form a resonant optical cavity. The order of the layersmay not be restricted as described above. To activate the laser, a biascurrent can be applied to top 0902 and bottom 0903 metal contacts. Uponapplication of the bias to the laser, light of a wavelength A 0907 istypically emitted from the edge of the laser. An exemplary edge emittingsemiconductor laser may include a GeSn quantum well active regionmaterial 0906 with GaAs barriers for near-infrared (IR) light emission0907, or their equivalents. The QW active region of the structure istypically capable of emitting a designed center wavelength over a widerange of possible wavelengths depending on a number of device designparameters including but not limited to the thickness and composition ofthe layer materials. Being able to tune light over the wide range ofwavelengths could be useful for a variety of applications.

The design and fabrication of this type of edge emitting laser structuremay utilize consideration of the material properties of each layerwithin the structure, including energy band structure and bandalignments, electronic transport properties, optical properties, systemsdesign, and the like. An edge emitting laser such as the exemplary onedescribed above may satisfactorily be wavelength tuned in the mannerpreviously described.

It may also be possible to omit the top metal 0902 and the bottom metal0903 and optically pump the edge emitter from the top, bottom or sidewith another laser that may have an emission wavelength shorter than theedge emitter 0901. This may simplify the process because metallizationof the laser 0901 can be avoided.

The second type of semiconductor laser, VCSELs, emits light normal tothe surface of the semiconductor wafer. The resonant optical cavity of aVCSEL can be formed with two sets of distributed Bragg reflector (DBR)mirrors located at the top and bottom of the laser, with the activeregion (which can be a quantum well, quantum dot, or quantum wireregion), sandwiched between the two Bragg reflectors. Note thedesignation of N DBR means that the DBR is doped N-type.

FIG. 10 is an exemplary schematic of the side view of a vertical cavitysurface emitting laser (“VCSEL”) 1001. A substrate 1006 can havedeposited layers of P-type distributed Bragg reflectors (“DBR”) material1003, and N-type distributed Bragg reflector material 1005. An activeregion 1004 is inserted in the optical confinement layer 1009 thensandwiched between the P DBR 1003 and the N DBR 1005 structures. Metalcontacts 1002, 1007 are provided for applying a bias to the laser. TheP-type DBRs 1003 and N-type DBRs 1005 form the resonant optical cavity.The order of the layers is not restricted as described above. Uponapplication of a current bias to the laser, light 1008 is typicallyemitted from the surface of the laser, which can be the bottom or top ofthe laser. A VCSEL laser 1001 such as the exemplary one described abovecan allow laser emission from the surface of the structure rather thanfrom the side or edge, as in the edge emitting laser of FIG. 9. Thoughthe diagram of an example of a VCSEL shows the light is coming out ofthe bottom, but could be designed so that light comes out of the top.

It can also be possible to omit the top metal 1002 and the bottom metal1007 and optically pump the VCSEL 1001 from the top or bottom withanother laser that can have an emission wavelength shorter than theVCSEL 1001. This may simplify the process because metallization of thelaser 1001 can be avoided.

These lasers can be called diode lasers or injection diode lasers andare two terminal devices. The HBT are three terminal devices. It ispossible to combine both structures to form the light emittingheterojunction bipolar transistor which can act as a three terminaldevice, but also can emit light. Such a device would allow forintegrated circuit designs that could transmit data optically and act ashigh speed switching transistors, all in a single device. Because thelight emitting transistor is a three terminal device, the extra terminalallows the biasing of the base collector junction to quickly collect thecharge carriers, and thereby out performing laser diodes and/or twoterminal devices.

For both the edge emitting laser 0901 and the VCSEL 1001, the inputcontrol to the lasers can be a current bias, voltage bias, or opticalpump techniques as described. Furthermore, both electrical injection andoptical pumping can be operated in continuous wave (CW), pulsed,synchronous, or asynchronous modes of operation.

The light emitting transistor or transistor laser could comprise abipolar transistor with a direct gap quantum well, quantum dot, orquantum wire inserted in the base/barrier region. The quantum well,quantum dot or quantum wire forms the collection region (active region)for electrons and holes to recombine to generate light.

In the following figures or tables, N⁺ refers to high N-type doping, N⁻refers to moderate N-type doping, P⁺ refers to high P-type doping, P⁻refers to moderate N-type doping, and UID refers to unintentionaldoping.

FIG. 11 shows a simple diagram of an NPN transistor laser 1100 showingthe three terminal device configuration with the correspondingemitter-base-collector designation, with a quantum well or quantum dotactive 1103 inserted into P base/barrier 1102 and 1104. Here emitter1101 and the collector 1105 can form the cladding regions for opticalconfinement of the light 1107 produced by recombination of the carriersin the quantum active region. The P base forms the barrier region forthe quantum well, quantum dot, or quantum wire and also the waveguidematerial. Because the transistor laser acts as a transistor and a laser,the emitter-base-collector needs to have dual functions for theelectrical and optical. For an NPN HBT laser the emitter has to injectelectrons into the base and also form the cladding layer for lightconfinement as designated by N emitter/cladding 1101. The base regionshould be heavily P-type doped and forms the barrier to the QW or QD1103 material and thus is designated by the P base/barrier 1102 and Pbase/barrier 1104. The P base/barrier 1102 and 1104 and the QW or QD1103 form the active region and the waveguide 1106 of the NPN transistorlaser 1100. To form for example, a light edge emitting transistor laser,a resonant cavity is typically formed by cleaving mirrors at the frontand back facets of the crystal to optically amplify the photonpopulation.

FIG. 12 shows a cross-sectional device depiction of an NPN edge emittingtransistor laser 1200. The device comprises an N⁺ substrate 1201 as thestarting point. A heavily doped N⁺ sub-collector 1202 is grown on the N⁺substrate 1201. Then a dual purpose lightly doped N− collector/bottomcladding 1203 layer is formed. Then a P⁺ base/barrier/opticalconfinement layer 1204 is grown and this also starts the formation ofthe waveguide region for the confinement of the light. Next the QW or QD1205 active region is grown, and then on top of this layer is the P⁺base/barrier/optical confinement layer 1206 which finishes the waveguideportion of the device. On top of this layer is then grown the N⁻emitter/upper cladding 1207 which provides the cladding finishing up thedevice. Metal contacts are placed at the N⁺ emitter contact 1208 via thetop metal 1209 contact, the P⁺ base/barrier/optical confinement layer1206 via the base metal 1210, and the N⁺ substrate 1201 via the bottommetal 1211. The resonant cavity is formed by the front cleaved crystalfacets 1214 and the back cleaved crystal facets 1213. Light 1212 isemitted from the front of the device. The device is biased in a standardNPN transistor configuration, but because of the inclusion of the QW orQD 1205, P⁺ base/barrier/optical confinement layer 1204 and 1206 and theN− collector/bottom cladding 1203 and N⁻ emitter/upper cladding 1207,the device forms a light emitting or laser transistor when properlydesigned. A typical way of making this structure is to use epitaxialtechniques to grow the basic layered structure then use standard deviceprocessing techniques to fabricate the full device. The laser includesquantum well, quantum dot, or quantum wire inserted into a base regionof the heterojunction bipolar transistor. The laser can require aresonant cavity to get optical gain, and typically this can be formedfrom the front and back cleaved facets of the semiconductor crystalwafer.

Vertical emission of light normal to the surface of the semiconductorwafer is also a useful configuration for transistor lasers. The resonantoptical cavity of a vertical transistor laser can be formed with twosets of distributed Bragg reflector (DBR) mirrors located at the top andbottom of the laser, with the active region (which can be a quantumwell, quantum dot, or quantum wire region), sandwiched between the twoBragg reflectors.

FIG. 13 shows a cross-sectional device depiction of an example of apossible configuration of a NPN VCSEL transistor laser 1300, where thelight is coming out of the top, but also could be designed so that lightcomes out of the bottom. The device can be grown on an N⁺ conductingsubstrate 1301, with the growth of a bottom N⁺ DBR 1302 stack whichforms the bottom mirror of the device. N⁻ collector 1303 is then grownon the bottom mirror. P⁺ base 1304 is then grown on the N⁻ collector1303, and also forms the barrier for QW or QD 1305 active region. QW orQD 1305 is deposited on P⁺ base 1304, and then P⁺ base 1306 is depositedon QW or QD 1305, finalizing the barrier material to the active regionfor quantum confinement effects. N⁻ emitter 1307 is then grown on P⁺base 1306. Then an N⁺ contact 1308 is deposited on N⁻ emitter 1307.Finally a dielectric mirror stack D DBR 1309 is deposited on N⁺ contact1308. VCSEL transistor laser 1300 is processed using standard techniquesof mesa etch and metallization to form the final structure, where metalcontacts emitter metal/aperture 1311 is deposited on N⁺ contact 1308.Emitter metal 1311 forms an aperture for light out 1310. Base metal 1312is deposited on P⁺ base 1306, and bottom metal 1313 is deposited on N⁺substrate 1301. NPN VCSEL transistor laser 1300 is operated as astandard bipolar device.

GeSiSn is alloy semiconductor of the constituent semiconductorsgermanium (Ge, which is an indirect semiconductor, with an energybandgap of 0.66 eV), silicon (Si, which is an indirect semiconductor,with an energy bandgap of 1.12 eV), and alpha tin or cubic tin (Sn,which is zero energy gap direct semiconductor). GeSiSn can be anindirect or direct energy bandgap semiconductor depending on the alloycomposition. A direct gap semiconductor has its conduction band minimumenergy and valence band energy maximum occur at the same crystalmomentum (k-space). If the location of the conduction band energyminimum and the valence band energy maximum occurs at different crystalmomentum (or different location in k-space), it is an indirectsemiconductor. Direct gap semiconductors are highly efficient forradiative recombination of electrons and holes, thus most light emittingdevices are fabricated from direct gap semiconductors.

GeSiSn semiconductors have been grown epitaxially by metalorganicchemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), ionimplantation follow by anneal, by pulse laser deposition (laserablation), but, liquid phase epitaxy, vapor phase epitaxy and variousother epitaxial growth techniques can be used to grow the GeSiSnmaterial described herein. Both N-type and P-type doping has beenachieved in GeSiSn layers.

FIG. 14 shows the energy band structure diagrams for the semiconductorsSi 1400, Ge 1401 and Sn 1402. The vertical axis is the Energy with unitsof (eV) and the horizontal axis is the Wavevector k. The energy bandstructure diagrams depict the available or unavailable (forbidden gap)energy levels for the charge carriers in the semiconductor. The plotshows energy on the vertical scale and the crystal momentum direction onthe horizontal scale. There are significant crystal momentum points “X,”“

” (Brillouin zone center) and “L.” Si 1400 is an indirect gapsemiconductor because the conduction band minima is at the “X” point andthe valence band maximum is at the “

” point. Ge 1401 is an indirect gap semiconductor because the conductionband minima is at the “L” point and the valence band maximum is at the “

” point. Sn 1402 is a semimetal or zero direct gap semiconductors withthe conduction band minima and valence band maxima at the “

” point. As Sn is added to Ge, the conduction band energy at the “

” point moves down faster than the conduction band energy at the “L”point, and thus, turning GeSn at some alloy composition turns into adirect gap semiconductor.

Ge is a group IV semiconductor and though it is an indirectsemiconductor, it has some properties that are advantageous toelectronic and photonic materials Ge 1401 has a local minimum at the “

” point of the conduction band. The lowest energy point in the Ge 1401conduction band is at the “L” point and is only 0.14 eV lower than the “

” point a room temperature. Various methods can be used to lower thegamma point below the L point such as introducing biaxial tensile strainor heavily N-type doping the Ge. However, by adding Sn to Ge, it ispossible to lower the bandgap but also form a direct gap semiconductor.One could employ both tensile strain and adding Sn to Ge to make adirect gap semiconductor. The other methodology to make Ge into a directgap semiconductor is by applying tensile strain on the Ge of greaterthan 1.4%. In some embodiments, the tensile strain can be a biaxialtensile strain.

In some examples, heterojunction bipolar transistors (HBT) can be adesirable device for greater power handling capability, higher powerefficiency, and lower signal distortion. The fabrication of a GeSiSnbased HBT structure enables a new transistor technology that cansignificantly outperform SiGe, GaAs, InP, and GaN transistors inhigh-power, high-frequency applications. The new HBT semiconductorstructure described herein exhibits a large valence band discontinuitybetween the emitter and base; has a low energy bandgap base (the termlow energy bandgap base typically refers to the relevant semiconductorswith bandgaps less than 1.0 eV, like GeSn or Ge or GeSi or GeSiSn orInGaAs or GaAsSb); and a second (double) heterojunction can be insertedbetween the base and collector with a good breakdown electric field.These attributes positively can impact several key device parameterssuch as collector-emitter breakdown voltage, DC current gain, and powergain cutoff frequency (F_(max)). The low bandgap GeSiSn base cansignificantly decrease transistor turn-on voltage and thereby increasethe power added efficiency of the device. The indirect gapsemiconductors there is the an added benefit that there is less baseradiative recombination enhancing the carrier transport across thedevice such as increases in the gain of the transistor.

FIG. 15 shows a graph of the collector current density J_(C) vs. theturn-on voltages (V_(BE)) of various HBT material systems. The figureshows a plot of the collector current density J_(C) (A/cm²) verticalscale versus base-emitter voltage V_(BE) (V), horizontal scale. Theplotted characteristics for several different heterojunction bipolartransistor (HBT) technologies are shown. The GeSiSn HBT structuredescribed herein can achieve low turn-on voltages 1501 when compared tothe technologies of Ge, InP/InGaAs, SiGe, GaAs, and GaN/InGaN. Thus thefollowing materials may be able to achieve low turn on voltages lessthan 1.0 V; GeSi latticed matched or near latticed matched to GaAs,GeSiSn latticed matched or near latticed matched to GaAs, for GaAs basedHBT geometries

For NPN heterojunction transistors, it is generally desirable for thebase region to be heavily P-type doped. This allows for the base sheetresistance to be minimized thus allowing for high frequency operation ofthe transistor. The GeSn alloy semiconductor can have the lowest turn-onvoltage because the bandgap of GeSn is less than that of Ge, which thancan be less than the relevant materials systems of GaN, GaAs, Si, InP,GaP, and AlAs. The GeSn base can be heavily doped P-type in someembodiments. When the hole concentration as measured by Hall Effect,high doping levels (>1×10¹⁹ cm⁻³) can be achieved in GeSn.

FIG. 16 shows the hole concentration of GeSn films as a function of Sn %as measured by Hall effect. The vertical axis is the hole concentration(cm⁻³) and the horizontal axis is the Sn %. From the hole concentrationdata vs. Sn % of FIG. 16, it is readily seen that GeSn can be P-typedoped at the highest levels of base doping which are greater than 1×10¹⁹cm⁻³. GeSn can achieve a large hole mobility (Ge hole mobility is about1800-2000 cm²/Vs, as compared to GaAs hole mobility 400 cm²/Vs) which isa precondition for making the base region thin.

By utilizing GeSiSn in the base material of a GaAs heterojunctionbipolar transistor, one can achieve low tunable turn-on voltage. At lowSi and Sn content, GeSiSn has all the advantages that a Ge base materialadds. For an NPN structure, Ge is desirable for the base region becauseit can be heavily doped P-type, it has the highest hole mobility(desirable for reducing the resistance of the base), also this holemobility can be increased by applying tensile or compressive strain, andits conduction band alignment is favorable with numerous semiconductors.Ge is an indirect semiconductor which results in less radiativerecombination in the base region of the transistor.

FIG. 17 shows the possible indirect energy bandgap of GeSiSn latticematched to GaAs or Ge as a function of Sn composition.

FIG. 18 shows a possible representative graph showing the GeSn directbandgap energy vs. lattice constant. The vertical axis shows the valuesof the Energy Bandgap (eV) and the horizontal axis shows the LatticeConstant (A). The dots and the line through the dots represent GeSndirect gap energy as a function of its lattice constant. The data forthe indirect to direct bandgap transition may occur near 7% Sn. Ge hasan indirect bandgap energy near 0.66 eV. GeSn may be indirect up toabout 7% Sn then becomes a direct gap semiconductor with an energy gapwhich may be 0.585 eV and a lattice constant of which may be 5.725 Å.The GeSn bandgap energy may be about 0.25 eV at about 20% Sn with alattice constant of about 5.835 Å. The emission wavelengths that canoccur in bulk direct gap GeSn range from about 2370 nm at 7% Sn to 5540nm at 20% Sn. For on-chip communications 1000 nm to 3000 nm isacceptable. For telecommunications applications, the typical wavelengthsused are 1300 nm and 1550 nm. These wavelengths can be achieved by usingquantum well or quantum dot GeSn materials. These low dimensionalstructures like two dimensional “2D” QW, one dimensional “1D” quantumwires, or zero dimensional “0D” quantum dot structures increase thelight emission energy due to quantum confinement effects.

It should be noted that GeSn is an alloy semiconductor and that Snpercentages can be varied from 0%≤Sn %≤20%.

GeSiSn materials are useful for photonic and quantum confinedstructures. Quantum confined structures such as quantum wells (QWs),quantum dots (QDs), and quantum wires structures add a new degree offreedom in making light emitting materials. Also GeSiSn is a tunablebandgap for enhancing optical barriers as in optical confinementstructures (OCL). One method of taking GeSiSn bulk material to getemission energies that cover this wide range is to use quantum well,quantum dot, or quantum wire technologies, because the light emission isthen dependent on quantum confinement or quantum size effects.

QDs form artificial semiconductor atoms with electronic “shells” thatcan be engineered to control their light absorption properties. Besidestheir novel electronic properties, QDs also have interesting materialproperties; their 3-dimensional shape allows greater strain relief atthe QD surfaces than for planar growth. GeSiSn QDs can be grown on Siwithout creating dislocations. Absorption over broad wavelengths comesfrom an ensemble of QDs that have sizes that vary statistically. Alsobecause GeSiSn at low Sn content starts as indirect material, it may bepossible to produce efficient light emission in QD structures withindirect gap semiconductors. The limitations of the indirect nature ofthe bandgap can be overcome by the formation of low-dimensionalstructures such as quantum dots because this method uses the spread ink-space caused by the quantum confinement to circumvent the indirectbandgap problem of the GeSiSn. Thus QDs are useful for producing lightemission in direct and indirect gap materials.

This 3-dimensional growth mode is a method of making zero dimensionalstructures (i.e., QD). For QDs to effectively provide light emission,the QD material is generally of a lower energy bandgap than the barriermaterial. The relatively low GeSiSn bandgap energy makes it a desirablestarting point for absorption in the near-IR and mid-IR. It is possibleby controlling the size of the GeSiSn quantum dots, to change theinterband (electron-hole recombination) to allow for energy transitionsin the near-IR to mid-IR.

FIG. 19 shows that the formation of quantum dot structures are a resultof ability of self-assembled GeSiSn by the Stranski-Krastanov (SK) orstrained layer epitaxy 1900 method that transitions from two dimensionalplanar growth 1901 to island growth 1902. In SK growth methodology alarger lattice constant semiconductor GeSiSn film 1903 is grown on asemiconductor with a smaller lattice constant Si 1904. Under properconditions two dimensional planar growth 1901 starts but quicklytransitions to island growth 1902 thus forming the GeSiSn QD 1905structure. Thus when a larger lattice constant semiconductor is grown ona semiconductor with a smaller lattice constant, the critical thicknessof the larger lattice constant layer is exceeded and QDs can form. Thelattice mismatch between the two layers should be generally greater than2% for dot formation. The mismatch of GeSiSn (latticed matched to GaAs5.65 Å) to Si with a lattice constant of 5.43 Å, may be about 4%. IfSiGe layers are used as the barrier depending on the Ge content in theSiGe, the lattice mismatch could be significantly reduced. Typicallyquantum dots are less than 15 nm, but they can range from 1 to 100 nm insize. Strained layer epitaxy 1900 is a methodology for growing quantumstructures with dissimilar lattice constant materials. After the 3Dgrowth of the QD, the QD layer usually has a barrier layer grown on topto finalize the quantum confinement.

FIG. 20 shows a flat band energy diagram of type II interband GeSn QDwith Si (bandgap energy approximately 1.12 eV) barriers 2000. The GeSn(bandgap energy less than about 0.66 eV) QD 2003 to Si 2002heterojunction which can be of a type II heterojunction band alignmentbut at higher Sn % can become type I alignment. The figure shows a typeII interband 2001 transition from the conduction band of the Si 2002 tothe GeSn QD hole level 2004. The energy bandgap is indicated inparenthesis below the material of interest. These type II interband 2001transitions allow the possibility of light emission. Type II energy bandalignments allow for emission energy levels that can be the closest tothe energy bandgap of the bulk semiconductor. Note the size L_(QD) 2005of the GeSn QD 2003 determines the energy difference of the type IIinterband transition. By changing the size L_(QD) one can change theemission wavelength of the structure.

FIG. 21 shows the possible range of emission wavelengths that areachievable in a type II GeSn quantum dot heterostructure with Sibarriers. The vertical axis is the wavelength (nm). The horizontal axisis the Quantum dot size (nm). This possible data represents the case forlow Sn % GeSn alloys. The graph shows that emission wavelengthsachievable depend on the size of the quantum dot. Note the wavelengthsare in the range of telecommunications. If the Sn % is increased, thewavelengths achieved gets longer.

A type I heterostructure band alignment can occur for a GeSiSn QD onalloy SiGe, because adding the Ge to Si barriers alter the Si bandstructure. The addition of Ge into Si increases the lattice constant,thus SiGe has a larger lattice constant than Si.

FIG. 22 shows type I alignment of the GeSiSn (bandgap energyapproximately less than 1.2 eV) QD with SiGe barriers 2200. The flatband energy diagram of GeSiSn QD 2203 with SiGe 2202 barriers which canbe of type I alignment. The figure shows a type I interband 2201transition from the conduction band of GeSiSn QD electron level 2204 tothe GeSiSn QD hole level 2205. These type I interband 2201 transitionsallow the possibility of light emission. Note the size L_(QD) 2206 ofthe GeSiSn QD 2203 determines the interband transition energy. Becausethe arrangement is of a type I heterostructure the emission energiesthat can be achieved are typically higher than in a type IIheterostructure. It is straightforward to calculate the range ofwavelengths achievable in the GeSiSn quantum dot with SiGe barriers.Basically the emission wavelengths that can be achieved for a type Ialignment may be shorter than that of type II QD heterostructures(energy bandgap is indicated in parenthesis below the material ofinterest). By utilizing SiGe 2202 one can change the Ge content of theSiGe thus changing the properties of the SiGe barrier layer to theGeSiSn QD 2203, thus in this structure the emission wavelengthsachievable depends on the QD size L_(QD), the composition of GeSiSn 2203material, and the ratio of Si to Ge in the SiGe 2202 barrier layer. Ifthe Ge content is high enough (greater than 50%) in the SiGe barrier itcan be possible to grow GeSiSn in a planar growth mode thus forming twodimensional growth or QWs.

The formation of QWs are more straightforward because the materials aregrown in a planar structure, and the QW can be coherently strained ornear latticed matched.

FIG. 23 shows the methodology of planar growth 2301 of the GeSiSn 2303QW region on the GaAs 2302 bottom barrier layer. GaAs 2302 bottombarrier layer has a may be lattice matched to GeSiSn 2303 or can begrown coherently or pseudomorphic on the GaAs 2302 (near latticematched). To finalize the QW layer a GaAs 2304 top barrier layer isgrown on the GeSiSn 2303 QW layer. Note that the barrier layer generallyhas a larger bandgap energy than the QW layer. The thickness of the QWregion and the band alignment to the barrier materials determine theallowable energy transitions.

FIG. 24 shows a flat band energy band diagram of a type I interbandGeSiSn QW with GaAs barriers 2400. The band alignment of GeSiSn QW 2403with GaAs 2402 barrier (bandgap energy of approximately 1.42 eV) can beof a type I heterojunction. GeSiSn (bandgap energy less thanapproximately 1.1 eV) can be grown latticed matched to GaAs or Ge(energy bandgap is indicated in parenthesis below the material ofinterest). It can also be coherently strained in tension or compression.As long as the GeSiSn thickness is less than the critical thickness,coherent planar or pseudomorphic growth can proceed on the GaAs or Gematerial. The Type I interband transitions are an excellent method forproducing the emission of light from semiconductor heterostructures. TheFIG. 24 shows a type I interband 2401 transition from the conductionband GeSiSn QW electron level 2404 to the GeSiSn QW hole level 2405.These type I interband 2401 transitions allow the possibility of lightemission. Note the size L_(QW) 2406 of the GeSiSn QW 2403 determines thetype I interband transition energy. Because the arrangement is of a typeI heterostructure the emission energies that can be achieved aretypically higher than in a type II heterostructure. Generally theemissions wavelengths that can be achieved for a type I alignment may beshorter than that of type II QW heterostructures.

For QW of a type I heterostructure the emission energies that can beachieved may be typically higher than in a type II heterostructure. TypeI interband transitions generally result in energy transitions that aregreater than the bulk GeSiSn transitions. Type II transitions can resultin energy transitions that can be less than the bulk GeSiSn transitions.Basically the emission wavelengths that can be achieved for a type Ialignment are shorter than that of type II QW heterostructures.

By utilizing a GeSiSn quantum well or a GeSiSn quantum dot in the baseregion of a transistor can achieve a light emitting HBT that can emitlight from 1000 nm to 5000 nm.

For an NPN HBT, utilizing a GeSiSn base region, has a tunable bandgapenergy depending on its composition.

FIG. 25 shows the general flat band energy diagram of an NPN GeSiSndouble heterojunction bipolar transistor. This shows the generalconfiguration of an NPN HBT with GeSiSn base 2500 region can include anN-type emitter of material 1 E_(G1) 2502, with a E_(G1) energy bandgapgreater than the GeSiSn 2501 and forms the P-type base region; then anN-type collector material 2 E_(G2) 2503 where the energy bandgap energyE_(G2) which can equal or be greater than the material 1 E_(G1) 2502.Furthermore, the conduction band offset energies ΔE_(C1) 2504 at theemitter base junction and the ΔE_(C2) 2505 at the base collectorjunction may be less than 0.1 eV. Small conduction band offsets betweenthe emitter-base junction and the collector-base junction are desirablefor electron transport. The valence band offset ΔE_(V1) 2506 at theemitter base junction should be as large as possible to ensure thatthere is no back injection of holes from the GeSiSn 2501 P-type base tomaterial 1 E_(G1) 2502 N-type emitter material. This GeSiSn structurecan be latticed matched or near latticed matched or coherently strainedto GaAs or Ge.

HBT performance can be improved, in some examples, by grading thecompositionally grading the base region to decrease the energy bandgapfrom the emitter base junction to the base collector junction. Thegrading of the base energy bandgap can create an electric field, whichcauses a reduction in the transit time of the charged carriers. This canbe accomplished by grading from the emitter base junction of the basestarting with GeSiSn and grading down to GeSn. The slope of the GeSiSncompositional grade in the base in this example can be varied fromlinearly or step graded. The compositionally graded GeSiSn may comprisefor example (not the only possibility) starting growth a near latticedmatch Ge₉₀Si_(0.8)Sn_(0.2) (to GaAs) then reducing the Si content whileincreasing the Ge content to have compressively strainedGe_(0.98)Sn_(0.2) at base-collector junction.

FIG. 26 shows the general flat band energy diagram of an NPN HBT with agraded GeSiSn—GeSn base 2600 region. Starting next to the N emittermaterial 1 E_(G1) 2602 with a Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) where z isless than 0.5, which is then graded to layer Ge_(1-b)Sn_(b) where b isless than 0.1 and this is represented by GeSiSn—GeSn 2601. Such astructure results in a field enhancement 2608 region. The generalconfiguration of this NPN HBT with the graded GeSiSn—GeSn 2601 P-typebase region can include an N-type emitter of material 1 E_(G1) 2602,with an E_(G1) energy bandgap greater than the GeSiSn—GeSn 2601 energybandgap range; then a GeSiSn—GeSn 2601 P-type base region; then a N-typecollector material 2 E_(G2) 2603 where the energy bandgap energy E_(G2)may equal or be greater than that of material 1 E_(G1) 2602.Furthermore, the conduction band offset energies ΔE_(C1) 2604 at theemitter base junction and the ΔE_(C2) 2605 at the base collectorjunction may be less than 0.1 eV. Having small conduction band offsetsbetween the emitter-base junction and the collector based junction isdesirable for electron transport. The valence band offset ΔE_(V1) 2606at the emitter base junction should be as large as possible to ensurethat there is no back injection of holes from the GeSiSn—GeSn 2601P-type base to material 1 E_(G1) 2602 N-type emitter material.

The importance of the base region of the HBT can be further elucidatedby the following example. A GaAs base HBT has a base thickness of 1000Å, for an equivalent device a GeSiSn base HBT, the base thickness couldbe halved to 500 Å with no detrimental results. The F_(t) for GeSiSn HBTmay be increased because of the thinner base. Because the GeSiSn baseresistivity could be for example 0.0026 ohm-cm at a high p-type dopinglevel and this may be 2 times less than GaAs resistivity 0.0052 ohm-cmat high doping, then for this example the parameter F_(max) wouldincrease by a factor of (2*F_(t))^(1/2).

Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) base material advantages. It can belatticed matched to GaAs and Ge for z<0.5. At low Sn % comprises similarproperties to Ge. GeSiSn may have a tunable bandgap energy from 0.66 eVto 1.1 eV, and thus can be used as low turn-on voltage base emitterjunction. GeSiSn (low Sn %<2%) may have a high hole mobility like Ge(2000 cm²/Vs) as compared to GaAs (400 cm²/Vs) and acceptors can beincorporated to high density (>1×10¹⁹ cm⁻³). GeSiSn base can be madeultra-thin (much less than 500 Å) while maintaining a low base sheetresistance (P-type base resistivity may be about 0.0026 ohm-cm) whichincreases current gain and decreases electron transit time. GeSiSn canbe heavily doped P-type (>2×10¹⁹ cm⁻³). GeSiSn for low Sn concentration,has shallow acceptors, so the hole concentration is generally equal tothe acceptor doping level and independent of temperature. The low basesheet resistance of GeSiSn results in a high F_(max). The surfacerecombination velocity may be low for P-type GeSiSn. GeSiSn at low Sn %is an indirect semiconductor thus direct recombination of carriers inthe base is reduced.

Another possible different embodiment may be an NPN HBT utilizing a GeSibase region.

FIG. 26A shows the general flat band energy diagram of an NPN GeSidouble heterojunction bipolar transistor. The alloy semiconductor GeSimay be latticed matched to various semiconductors like GaAs or Ge, etc.This shows the general configuration of an NPN HBT with GeSi base 2600Aregion include an N-type emitter of material 1 E_(G1) 2602A, with aE_(G1) energy bandgap greater than the GeSi 2601A and forms the P-typebase region; then an N-type collector material 2 E_(G2) 2603A where theenergy bandgap energy E_(G2) which can equal or be greater than thematerial 1 E_(G1) 2602A. Furthermore, the conduction band offsetenergies ΔE_(C1) 2604A at the emitter base junction and the ΔE_(C2)2605A at the base collector junction may be less than 0.1 eV. Smallconduction band offsets between the emitter-base junction and thecollector-base junction may be desirable for electron transport. Thevalence band offset ΔE_(V1) 2606A at the emitter base junction should beas large as possible to ensure that there is no back injection of holesfrom the GeSi 2601A P-type base to material 1 E_(G1) 2602A N-typeemitter material. This GeSi structure can be latticed matched between toGaAs or Ge and can also be in a coherently strained structure (nearlatticed matched).

A light emitting heterojunction bipolar transistor can be formed byplacing a GeSiSn quantum well or quantum dot in the base region of aheterojunction transistor. This is a methodology for the formation of alight emitting transistor or transistor laser.

FIG. 27 shows the resulting flat band energy diagram of an NPN HBT withGeSiSn QD inserted in the P-type base region 2700 for the initialformation of a light emitting transistor. Material 3 E_(G3) 2703 is theP-type base region and forms the barrier to the GeSiSn QD 2707 to getquantum confinement and also can serve as the waveguide material. Thematerial 3 E_(G3) 2703 bandgap energy should be greater than the bandgapenergy of the bulk GeSiSn material which may be less than 1.1 eV. TheN-type emitter material 1 E_(G1) 2701 and N-type collector material 2E_(G2) 2702 can serve as the cladding layers of the transistor laser orlight emitting transistor (LET). The general configuration of an NPN HBTcan include an N-type emitter of material 1 E_(G1) 2701, with an E_(G1)energy bandgap greater than material 3 E_(G3) 2703 P-type base region.The N-type collector material 2 E_(G2) 2702 should have a bandgap energyE_(G2) equals to the material 1 E_(G1) 2701 or can be much larger. Theconduction band offset energies ΔE_(C1) 2704 at the emitter basejunction and the ΔE_(C2) 2705 at the base collector junction need not besmall because a type I alignment assists in funneling the carriers intothe waveguide and to the GeSiSn QD 2707. The valence band offset ΔE_(V1)2706 at the emitter base junction should be as large as possible toensure that there is no back injection of holes from the P-type base tomaterial 1 E_(G), 2701 N-type emitter material.

Variations could include grading of the quantum region in the basematerial of such a device.

FIG. 28 shows a slight variation to FIG. 27 where the flat band energydiagram of NPN HBT 2800 has a GeSiSn QW or QD 2807 inserted in the baseregion where the barrier layer has been graded 2808 from the P-basematerial 3 E_(G3) 2703.

Exemplary Configurations: Note these are exemplary heterojunctionbipolar transistor and/or transistor laser configurations or lightemitting transistor and are used to illustrate the purposes and uses ofthe various configurations. In various embodiments, the GeSiSn baseregion can be replaced by a graded GeSiSn to GeSn base region.

Exemplary Configuration 1: An NPN structure of a GaAs Emitter-GeSiSnBase-GaAs Collector symmetric double heterojunction transistor.Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) can be latticed matched or near latticedmatched or strained to GaAs for z<0.5. Typically GaAs HBTs have been thestandard of the industry. The device elucidated in this example caninclude a symmetric double heterojunction GaAs—GeSiSn—GaAs HBT device.This device can have desirable base characteristics with a low voltagebase turn-on (bandgap energy is <1.0 eV depending on the Si % and Sn %)region and a symmetric double heterojunction thus eliminating the offsetvoltage in the transistor output characteristic that reduces power addedefficiency.

FIG. 29 illustrates an exemplary flat band energy diagram of a GaAsEmitter-GeSiSn Base-GaAs Collector NPN symmetric double HBT 2900.Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) can be latticed matched to GaAs for z<0.5and may have a tunable bandgap energy from 0.66 eV to 1.1 eV (energybandgap is indicated in parenthesis below the material of interest). Forlow Sn % less than equal to 2% the bandgap of GeSiSn may be less than0.8 eV. For example the composition Ge_(0.90)Si_(0.08)Sn_(0.02) may havea bandgap energy of near 0.78 V. At this composition the conduction bandoffset may be approximately ΔE_(C)<0.1 eV 2901 which may result in alarge valence band offset ΔE_(V) 2902. Near zero conduction band offsetsare generally less than 0.1 eV. This unique arrangement of materialscombines the high transconductance of heterojunction bipolar transistor(HBT) technology, and a desirable emitter-base heterojunction (widebandgap GaAs 2904 emitter on a narrow bandgap high conductivity P⁺GeSiSn 2903 base). The large valence band discontinuity between the GaAsemitter and GeSiSn base allows one to lightly N dope the GaAs emitter,while heavily doping P base GeSiSn 2903. The large valence banddiscontinuity prevents the back injection of holes into the emitter thuspreventing the degradation in the gain or beta of the transistor. TheGaAs 2905 collector provides a reasonable base collector breakdownbecause the bandgap energy of the GaAs is approximately 1.42 eV.

This unique arrangement of materials combines the high transconductanceof heterojunction bipolar transistor (HBT) technology, with thebreakdown voltage (using a GaAs collector), and a desirable emitter-baseheterojunction (wide bandgap GaAs emitter on a narrow bandgap highconductivity P-type GeSn base). The combination of a low bandgap (<0.8eV depending for Sn %<2%) GeSiSn base coupled with a wide bandgap GaAs(can be about 1.42 eV) collector can be used for high speed powerapplications. This symmetric double heterojunction bipolar transistordevice results in a minimum in the zero offset voltage in themeasurement of the collector current vs. the collector-emitter voltageas a function of the stepped voltage bias of the base-emitter junction,which is desirable for improving the power added efficiency of the NPNheterojunction bipolar transistors. The use of efficientGaAs—GeSiSn—GaAs transistors can significantly enhance battery lifewhile also enabling operation at high frequency response, which can bedesirable when used as RF power amplifiers for wireless devices orcellular phone applications.

FIG. 30 shows an exemplary cross-sectional device depiction ofembodiment of an NPN GaAs—GeSiSn—GaAs symmetric double HBT 3000. Thisdevice depiction shows the standard HBT in a mesa configuration. One cangrow this device epitaxially with a variety of techniques like molecularbeam epitaxy (MBE), metalorganic chemical deposition (MOCVD), pulsedlaser deposition (PLD) or other epitaxy methods. One starts with a highquality single crystal semi-insulating GaAs substrate 3001. An N⁺ GaAssub-collector 3002 is grown first, followed by the N⁻ GaAs collector3003, then the GeSiSn Base 3004 (which may be grown by MBE, MOCVD, PLD,etc.). An N⁻ GaAs emitter 3005 is grown on the P-type base, followed bythe N⁺ GaAs contact layer 3006. Contact is made to the device throughthe emitter metal 3007, the base metal 3008, and the collector metal3009. The structure may be lattice matched or coherently strained.

The base can be compositionally graded from GeSiSn—GeSn to have fieldenhancement of the carriers.

FIG. 31 illustrates an exemplary flat band energy diagram of an NPNstructure of a GaAs Emitter-graded GeSiSn—GeSn Base-GaAs Collectordouble HBT 3100. FIG. 31 is a variation on FIG. 29, by including thecompositionally graded GeSiSn—GeSn 3101 P-type base region; thisstructure creates an electric field that accelerates the electronsacross the base to the collector, thus creating the field enhancement3102 region. Starting next to the N emitter GaAs 3103 with aGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) where z is less than 0.5 which may belatticed matched near latticed matched or strained to GaAs, which can begraded to layer Ge_(1-b)Sn_(b) where b is less than 0.1 and this isrepresented by GeSiSn—GeSn 3101. Such a structure results in a fieldenhancement 3102 region. The general configuration of this NPN HBT withthe graded include an N-type emitter of GaAs 3103, then a GeSiSn—GeSn3101 P-type base region with an energy bandgap range that may be from1.0 eV to less than 0.66 eV, then a N-type GaAs collector 3106.Furthermore, the GaAs conduction band offset energies ΔE_(C1) 3104 atthe emitter base junction and the ΔE_(C2) 3107 at the base collectorjunction may be less than 0.1 eV. The ΔE_(V1) 3105 may be large to stopback injection of carriers.

Table 1 shows an exemplary structure that could be grown for an NPNstructure of a GaAs Emitter-GeSiSn Base-GaAs Collector doubleheterojunction transistor. Note the table shows the variation of GeSiSnbase region or a compositionally graded GeSiSn—GeSn base region, eitherwhich can be used in the structure. Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) canbe latticed matched to GaAs for 0≤z≤0.5. TheGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) can be a near lattice matched ofcoherently strained structure. Note the compositionally gradedGeSiSn—GeSn layer can comprise at the emitter-base interface startingwith a lattice matched or near latticed matched or strainedGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAs and then compositionally gradingthe GeSiSn by reducing the Si % and increasing Sn % to GeSn at thecollector interface. The grading range can be from GeSiSn at theemitter-base junction to GeSn at the base-collector junction in variouscompositions. GeSiSn is an alloy semiconductor Ge_(1-x-y)Si_(x)Sn_(y)and GeSn (Ge_(1-b)Sn_(b)) is a component semiconductor of GeSiSn. Notethe dopants listed are only one of many possible dopants, and doespreclude the use of other dopants and doping values are only nominalvalues but can take on many variations. The thicknesses are allexemplary and can take on many different values.

TABLE 1 Exemplary Epitaxial Structure of NPN GaAs—GeSiSn—GaAs HBT. LayerLayer Name Description Comment 1 N⁺ Cap ~1000 Å InGaAs (can be Te-doped>10¹⁹ cm⁻³) Te = tellurium InGaAs layer may be relaxed 2 N⁻ Emitter Cap~1500 Å GaAs (can be Si-doped ~5 × 10¹⁸ cm⁻³) Si = silicon, otherdopants possible 3 N⁻ Emitter ~500 Å GaAs (can be Si-doped ~3 × 10¹⁷cm⁻³) 4 P⁺ Base ~500 Å Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z) Latticed matched 0≤ Si % ≤ 40% or 0 ≤ Sn % ≤ 10% Can be compositionally Thickness range100 Å-5000 Å graded GeSiSn—GeSn 5 N⁻ Collector ~10000 Å GaAs (can beSi-doped ~1 × 10¹⁶ cm⁻³) 6 N⁺ Sub-Collector ~5000 Å GaAs (can beSi-doped ~5 × 10¹⁸ cm⁻³) 7 Buffer ~500 Å GaAs Can be undoped or N- typedoped 8 GaAs semi-insulating or conducting substrate Substrate Note thedopants listed are only one of many possible dopants, and does precludethe use of other dopants and doping values are only nominal values butcan take on many variations. The thicknesses are all exemplary and cantake on many different values.

It should be noted where the subscripts are missing GeSiSn refers toGe_(1-x-y)Si_(x)Sn_(y), GeSi refers to Ge_(1-a)Si_(a), GeSn refers toGe_(1-b)Sn_(b), and SiSn refers to Si_(1-c)Sn_(c).Ge_(1-x-y)Si_(x)Sn_(y) can be comprised materials of Ge_(1-a)Si_(a),Ge_(1-b)Sn_(b), and Si_(1-c)Sn_(c) at various compositions which mayalso be latticed matched or near latticed matched or strained to GaAs orGe. Ge_(1-x-y)Si_(x)Sn_(y) may be written in the following formGe_(1-z)(Si_(1-k)Sn_(k))_(z). Where the value of k may be equal to 0.2and may have a range of 0≤k≤0.4. This designation form may be useful forthe following materials composition Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) wherez is 0≤x≤0.5 may be lattice matched or near latticed matched orcoherently strained or pseudomorphic to Ge or GaAs semiconductors. Thesubscripts for example Si_(0.8) and Sn_(0.2) may be empirical values andcan have a degree of variation. Thus GeSiSn may have a range of Si andSn contents for Ge_(1-x-y)Si_(x)Sn_(y) to lattice matched condition toGaAs and Ge.

Exemplary GaAs advantages: The large valence band offset between GaAsemitter and GeSiSn base can stop back injection of holes into theemitter. This allows for low N-type doping of the emitter and highP-type doping of the base, thus lowering base emitter capacitance whilestill achieving sizable current gain. GeSiSn can be latticed matched toGaAs (˜5.65 Λ), which enables dislocation free growth.

The latticed matched GaAs—GeSiSn emitter base junction may have a largevalence offset (for example >0.7 eV). This eliminates the back injectionof holes to the emitter from the base, which reduces the gain of thetransistor. The base may be doped heavily P-type (typically >1×10¹⁹cm⁻³), with such high doping of the base, the emitter valence bandoffset blocks the holes even though the base doping may be much higherthan the N-type emitter doping low 10¹⁷ cm⁻³). Furthermore, becauseGeSiSn may have low resistivity of 0.0026 ohm-cm at high p-type doping,one can decrease the thickness of the base significantly, while stillmoderately increasing the base sheet resistance value. The frequencyresponse of the device may be related to the F_(t) and F_(max). Therelationship between transit frequency F_(t) and the maximum oscillationfrequency F_(max) is as follows for an HBT:F_(max)=(F_(t)/8πR_(B)C_(CB))^(1/2). The transit frequency F_(t) may bethe inverse of the time for the electron to traverse the emitter, base,and collector. The parameters R_(B) and C_(CB) refer to the base sheetresistance and the capacitance of the collector base junction. Theparameter F_(max) is the unity power gain frequency and indicates themaximum frequency with power gain from a device. The transit frequencycan be further improved by having a higher saturation velocity for thecollector.

It should be noted that there are many types of N-type and P-typedopants. For standard III-V semiconductors like GaAs, InP, InGaAs,InGaP, the N-type dopants may be Si, Ge, Sn, Pb, S, Se, Te. The P-typedopants for standard III-V semiconductors may be C, Zn, Be, Mg. Commondopants for group IV semiconductors like GeSn, Ge, Si, SiGe, GeSiSn forN-type dopants may be P, As, Sb. The P-type dopants may be B, Al, Ga.Also the concentrations of the dopants vary depending on transistordesign and those listed in the table are only possible guidelines.

Also designations such as N⁺ reference highly N-type doped material andN⁻ lightly doped N-type material. Also designations such as P⁺ referencehighly P-type doped material and P⁻ lightly doped P-type material.Unintentionally doped material can be denoted as UID.

FIG. 31A illustrates an possible example of an exemplary flat bandenergy diagram of a GaAs Emitter-GeSi Base-GaAs Collector NPN symmetricdouble HBT 3100A. For example Ge_(0.98)Si_(0.02) can be latticed matchedto GaAs and may have a bandgap energy of approximately 0.7 eV (rangingfrom 0.67 eV to 0.72 eV). Note for this example the conduction bandoffset ΔE_(C)<0.1 eV 3101A with a large valence band offset ΔE_(V)>0.1eV 3102A. Near zero conduction band offsets are generally less than 0.1eV. This unique arrangement of materials combines the hightransconductance of heterojunction bipolar transistor (HBT) technology,and a desirable emitter-base heterojunction (wide bandgap GaAs 3104Aemitter on a narrow bandgap high conductivity P⁺ GeSi 3103A base). Thelarge valence band discontinuity between the GaAs emitter and GeSi baseallows one to lightly N dope the GaAs emitter, while heavily doping Pbase GeSi 3103A. The large valence band discontinuity prevents the backinjection of holes into the emitter thus preventing the degradation inthe gain or beta of the transistor. The GaAs 3105A collector provides areasonable base collector breakdown because the bandgap energy of theGaAs is 1.42 eV.

In some examples, to fabricate a light emitting bipolar transistor mayrequire an insertion into the high Sn % (>5%) GeSiSn P-type base region(or GaAs base), a GeSn quantum dot QD or quantum well QW.Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) can be latticed matched to GaAs forz<0.5. The GeSiSn layer may be latticed matched to GaAs or coherentlystrained.

FIG. 32 shows an exemplary flat band energy diagram of an NPN transistorlaser or LET structure with a GeSn QW or QD active region in a high Sn %GeSiSn P⁺ base/barrier material 3200. The high Sn % GeSiSn 3201 and 3202forms the P⁺ base and also acts as a barrier layer for quantum confinethe electrons and holes in the GeSn QW or QD 3203. QWs are formed byhaving a large energy bandgap material surrounded by a low energybandgap material which results in two dimensional electron confinement.For a QD the growth of a large lattice constant material on a smallerlattice constant material results in strained layer epitaxy allowing theself-assembled three dimensional island growth. Typical thickness ofquantum wells can be about 10 nm but they can range from 1 nm to 50 nmdepending on the wavelength of interest that needs to be produced.Typical quantum dot diameters are in the range of 1 nm-20 nm, but aredependent on the wavelength of light that needs to be emitted. The GeSnQW or QD 3203 inserted into a high Sn % GeSiSn 3201 & 3202 base/barrierserves for the collection region for electrons and holes to recombine togenerate light. The GeSiSn 3201 & 3202 also serve as the opticalconfinement layer and the waveguide material. The GaAs 3204 & 3205serves as the emitter/cladding and collector/cladding material for thisstructure. The cladding serves as funneling carriers into theactive/waveguide region and traps the emit light in the waveguidestructure. The large energy bandgap difference between the GaAs 3204 &3205 and the GeSiSn 3201 & 3202 ensures a large index of refractiondifference at the N⁻ emitter/cladding 3206 and P⁺ base/barrier 3207junction and a large index refraction difference at the P⁺ base/barrier3208 and N⁻ collector/cladding 3209, thus making an excellent waveguide3210 to optically confine the light produced by the active region.

FIG. 33 shows a possible cross-sectional device depiction of an NPNtransistor laser structure or light emitting transistor with a GeSn QWor QD 3306 active region in a high Sn % GeSiSn P-type base/barriermaterial 3300. The structure can be grown on N⁺ GaAs conductingsubstrate 3303, which is the seed crystal to grow the full structure. N⁻GaAs collector/cladding 3304 and the N⁻ GaAs emitter/cladding 3308 dodual functions of optical confinement of the light 3309 produced andcontrolling the flow of electrons and holes. The P⁺ GeSiSn base 3305 and3307 forms the barrier material for the GeSn QW or QD 3306, and alsoprovide the waveguide material. The laser can require a resonant cavityto get optical gain, and typically this can be formed from the frontcleaved facets 3302 and back cleaved facets 3301 of the semiconductorcrystalline structure.

Table 2 shows an exemplary epitaxial structure of an NPN light emittingstructure with a GeSn QW or QD active region in a GeSiSn P-typebase/barrier HBT.

TABLE 2 Exemplary epitaxial structure of NPN light emitting structurewith a GeSn QW or QD active region in a GeSiSn P-type base/barrier HBT.Layer Layer Name Description Comment 1 N⁺ Cap ~1000 Å InGaAs (Te-doped>10¹⁹ cm⁻³) 2 N⁻ Emitter/Cladding ~1000 Å GaAs (Si-doped ~3 × 10¹⁷ cm⁻³)3 P⁺ Base/Barrier ~450 Å GeSiSn (B-doped >10¹⁹ cm⁻³) B = boron, high Sn% May be lattice matched 4 QW ~100 Å GeSn For light emission or QD Sncontent can be: 0 ≤ Sn % ≤ 20% 1000 nm-5000 nm QW (Sn % ~0% to 10% GeSn)QW thickness range 10 Å-1000 Å QD (Sn % ~10% to 20% GeSn) QD size range10 Å-500 Å 5 P⁺ Base/Barrier ~450 Å GeSiSn (B-doped >10¹⁹ cm⁻³) B =boron, high Sn % May be lattice matched 6 N⁻ Collector ~1000 Å GaAs(Si-doped ~1 × 10¹⁶ cm⁻³) 7 N⁺ Sub-Collector ~500 Å GaAs (Si-doped ~5 ×10¹⁸ cm⁻³) 8 N⁺ Buffer ~500 Å GaAs (Si-doped ~5 × 10¹⁸ cm⁻³) 9 GaAs N⁺conducting or semi-insulating Substrate Note the p+ base barriers may belattice matched or coherently strained Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z)with tunable band gaps based on the z value to GaAs. Note the dopantslisted are only one of many possible dopants, and does preclude the useof other dopants and doping values are only nominal values but can takeon many variations. The thicknesses are all exemplary and can take onmany different values.

The semiconductor alloy In_(0.49)Ga_(0.51)P (InGaP refers to alloysemiconductor through the text) can be lattice matched to GaAs. This isthe literature composition values of InGaP that can be grown latticematched to GaAs, but may have variations in actual practice. Also thecomposition of InGaP can be varied to be tensile strained or compressivestrained to the GaAs. InGaP can be grown in a disordered phase, orderedphase, or a combination of the two. The disordered InGaP phase may havea bandgap energy of 1.9 eV. The bandgap of the ordered InGaP may beabout 1.85 eV. In some examples, to fabricate a light emitting bipolartransistor may require an insertion into the GaAs base region a GeSnquantum well, quantum dot, or quantum wire layer or GeSiSn quantum well,quantum dot, or quantum wire layer. The GaAs is the p type base materialbut also acts as a barrier layer to quantum confine the electrons andholes in the QW and QDs or quantum wires. QWs are formed by having alarge energy bandgap material surrounded by a low energy bandgapmaterial which results in two dimensional electron confinement. For a QDthe strained layer growth results in three dimensional electronconfinement. Typical thicknesses of quantum wells are about 100 Å butthey could be larger or less than that thickness depending on theemission wavelength desired. Typical quantum dot diameters are in therange of 1 nm-20 nm, but are dependent on the wavelength of light thatneeds to be emitted.

FIG. 34 shows an exemplary flat band energy diagram of an NPN transistorlaser or LET structure with a GeSiSn QW or QD active region in a GaAs P⁺base/barrier material 3400. The In_(0.49)Ga_(0.51)P disordered 3401 &3405 serves as the N⁻ emitter/cladding and N⁻ collector/cladding layers.Note the relevant band discontinuities ΔE_(C), ΔE_(V) are shown in thefigure and are approximate values and may have a wide variation. Thelaser includes a GeSiSn QW or QD 3403 active region for the collectionregion for electrons and holes to recombine to generate light, which isinserted into a P⁺ GaAs base/barrier 3402 & 3404, which also serves asthe barrier layer of the GeSiSn QW or QD 3403 active region, thusserving also as the optical waveguide 3410 material. The large energybandgap difference between the In_(0.49)Ga_(0.51)P disordered 3401 &3405 and the GaAs base/barrier 3402 & 3404 ensures a large index ofrefraction difference at the N⁻ emitter/cladding 3406 and P⁺base/barrier 3407 junction and a large index refraction difference atthe P⁺ base/barrier 3408 and N⁻ collector/cladding 3409, thus making anexcellent waveguide 3410 to optically confine the light produced by theactive region. GeSn QW or QD could also be used as the active region.

FIG. 35 shows a possible cross-sectional device depiction of an NPN edgeemitting transistor laser or light emitting structure with a GeSiSn QWor QD active region in a GaAs P⁺ base/barrier material 3500. A GeSiSn QWor QD 3506 active region in a P⁺ GaAs base 3505 & 3507 which alsofunctions as the barrier material for the QW or QD. This is anexceptional device because the type I discontinuities form an excellentoptical and electrical confining structure. The structure can be grownon N⁺ GaAs conducting substrate 3503, which is the seed crystal to growthe full structure. N⁻ InGaP (disordered) collector/cladding 3504 andthe N⁻ InGaP (disordered) emitter/cladding 3508 do dual functions ofoptical confinement of the light 3509 produced and controlling the flowof electrons and holes. P⁺ GaAs base 3505 & 3507 form the barriermaterial for GeSiSn QW or QD 3506, and also provide the waveguidematerial. The laser can require a resonant cavity to get optical gain,and typically this can be formed from the front cleaved facets 3502 andback cleaved facets 3501 of the semiconductor crystalline structure.

Table 3 shows an exemplary table of the epitaxial structure of an NPNlight emitting GeSiSn QW or QD active region in a GaAs P-typebase/barrier HBT.

TABLE 3 An Exemplary epitaxial structure of an NPN edge emittingtransistor laser structure with a GeSiSn QW or QD active region in aGaAs P-type base/barrier material. Layer Layer Name Description Comment1 N⁺ Cap ~1000 Å InGaAs (Te-doped >10¹⁹ cm⁻³) 2 N⁻ Emitter/Cladding~5000 Å In_(0.49)Ga_(0.51)P (Si-doped ~3 × 10¹⁷ cm⁻³) Disordered 3 P⁺Base/Barrier ~500 Å GaAs (B-doped >10¹⁹ cm⁻³) 4 QW ~55 Å GeSiSn Forlight emission or QD QW Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z) where z < 0.51000 nm-5000 nm QW thickness range 10 Å-1000 Å QD GeSiSn with high Sn %~10% to 20% QD size range 10 Å-500 Å 5 P⁺ Base/Barrier ~500 Å GaAs(B-doped >10¹⁹ cm⁻³) 6 N⁻ Collector/Cladding ~5000 Å In_(0.49)Ga_(0.51)P(Si-doped ~3 × 10¹⁷ cm⁻³) Disordered 7 N⁺ Sub-Collector ~500 Å GaAs(Si-doped ~5 × 10¹⁸ cm⁻³) 8 N⁺ Buffer ~500 Å GaAs (Si doped ~5 × 10¹⁸cm⁻³) 9 N⁺ GaAs conducting substrate Crystalline Note for the QW a nearlattice matched or strained Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z) to GaAs maybe used, with tunable band gaps based on the z value. For the QDs a highSn % GeSiSn layer would be used. Note the dopants listed are only one ofmany possible dopants, and does preclude the use of other dopants anddoping values are only nominal values but can take on many variations.The thicknesses are all exemplary and can take on many different values.

The transistor laser has the integrated features of both the transistorand the laser. It is closely similar to a light emitting transistorexcept it has light amplification. From such a structure it can bestraightforward to simplify the structure and grow a separateconfinement heterostructure (SCH) laser.

FIG. 36 shows an exemplary flat band energy diagram of an SCH laserutilizing a GeSn QW or QD region 3600 located in UID high Si GeSiSnbarrier/OCL layer 3602 & 3604 region with P⁺ GaAs 3601 cladding and N⁺GaAs 3605 cladding layers. This structure represents a PN junction ordiode with an unintentionally doped (UID) active region and opticalconfinement region between the P⁺ GaAs 3601 and N⁺ GaAs 3605 cladding.The UID Ge 3602 and 3604 forms the barrier material for the GeSn QW orQD 3603 active region. The combination of the barrier and active regionforms the waveguide 3606 of the laser. The P⁺ GaAs 3601 cladding regionserves for injection of the holes and for the optical confinement of thelight emitted from the active region. The N⁺ GaAs 3605 cladding regionserves for injection of the electrons and for the optical confinement ofthe light emitted from the active region. Though this depicts asymmetric structure it can be also asymmetric.

FIG. 37 shows a cross-sectional depiction of a SCH ridge laser utilizinga GeSn QW or QD region 3700 located in UID GeSiSn barrier/OCL regionwith P-type GaAs and N-type GaAs cladding. The structure can be grown onN⁺ GaAs conducting substrate 3703. N⁺ GaAs cladding 3704 serves for theinjection of electrons into the active region and the bottom claddingfor the optical confinement of the light emitted from the active region.The P⁺ GaAs cladding 3708 serves for the injection of holes into theactive region, and the top cladding for optical confinement of the light3709 emitted from the active region. The UID GeSiSn 3705 & 3707 formsthe barrier material for the GeSn QW or QD 3706, and also provide theOCL material. The laser can require a resonant cavity to get opticalgain, and typically this can be formed from the front cleaved facets3702 and back cleaved facets 3701 of the semiconductor crystallinestructure. The ridge structure provides the vertical guiding of thecurrent into the active region.

Table 4 shows an exemplary epitaxial structure SCH injection diode laserwith a GeSn QW or QD region with GeSiSn barriers.

TABLE 4 Exemplary epitaxial structure SCH injection diode laser with aGeSn QW or QD region with GeSiSn barriers. Layer Layer Name DescriptionComment 1 P⁺ Cap ~1000 Å GaAs (Zn doped >10¹⁹ cm⁻³) 2 P⁺ Cladding ~10000Å GaAs (Zn doped ~1 × 10¹⁸ cm⁻³) 3 Barrier/OCL ~450 Å GeSiSn UID 4 QW~100 Å GeSn For light emission or QD QW (Sn % ~0% to 10% GeSn) 1000nm-5000 nm QW thickness range 10 Å-1000 Å QD (Sn % ~10% to 20% GeSn) QDsize range 10 Å-500 Å 5 Barrier/OCL ~450 Å GeSiSn UID 6 N⁺ Cladding~10000 Å GaAs (Si-doped ~1 × 10¹⁸ cm⁻³) 7 N⁺ Buffer ~5000 Å GaAs(Si-doped ~5 × 10¹⁸ cm⁻³) 8 GaAs N⁺ conducting substrate CrystallineNote for the barrier/OCL a near lattice matched or strainedGe_(1−z)(Si_(0.8)Sn_(0.2))_(z) to GaAs may be used, with tunable bandgaps energy based on the z value. Note the dopants listed are only oneof many possible dopants, and does preclude the use of other dopants anddoping values are only nominal values but can take on many variations.The thicknesses are all exemplary and can take on many different values.

A variation of the laser structure could incorporate GeSn QW or QD;GeSiSn QW or QD region in a UID GaAs barrier/waveguide region, andutilizing latticed match InGaP as the cladding material.

FIG. 38 shows an exemplary flat band energy diagram of an SCH diodelaser utilizing a GeSn QW or QD; or GeSiSn QW or QD region 3800 locatedin UID GaAs 3802 & 3804 barrier/OCL region with P⁺ InGaP 3801 disorderedand N⁺ InGaP 3805 disordered cladding. This structure represents a PNjunction or diode with an unintentionally doped (UID) active region andoptical confinement region between the P⁺ InGaP 3801 disordered and N⁺InGaP 3805 disordered cladding. The UID GaAs 3802 & 3804 forms thebarrier material for the GeSn QW or QD; or GeSiSn QW or QD 3803 activeregion. The combination of the barrier and active region forms thewaveguide 3806 of the laser. The P⁺ In_(0.49)Ga_(0.51)P disordered 3801top cladding region serves for injection of the holes and for theoptical confinement of the light emitted from the active region. The N⁺In_(0.49)Ga_(0.51)P disordered 3805 bottom cladding region serves forinjection of the electrons and for the optical confinement of the lightemitted from the active region. Though this depicts a symmetricstructure it can be also asymmetric.

Table 5 shows an exemplary epitaxial structure SCH injection diode laserwith a GeSn QW or QD region with GaAs barriers.

TABLE 5 Exemplary epitaxial structure SCH injection diode laser with aGeSn QW or QD region with GaAs barriers. Layer Layer Name DescriptionComment 1 P⁺ Cap ~1000 Å GaAs (Zn doped >10¹⁹ cm⁻³) 2 P⁺ Cladding ~10000Å In_(0.49)Ga_(0.51)P (Zn-doped ~1 × 10¹⁸ cm⁻³) Disordered 3 Barrier/OCL~450 Å GaAs UID 4 QW ~10-1000 Å GeSn For light emission or QD QW (Sn %~0% to 10% GeSn) 1000 nm-5000 nm QW thickness range 10 Å-1000 Å QD (Sn %~10% to 20% GeSn) QD size range 10 Å-500 Å 5 Barrier/OCL ~450 Å GaAs UID6 N⁺ Cladding ~10000 Å In_(0.49)Ga_(0.51)P (Si-doped ~1 × 10¹⁸ cm⁻³)Disordered 7 N⁺ Buffer ~5000 Å GaAs (Si-doped ~5 × 10¹⁸ cm⁻³) 8 GaAs N⁺conducting substrate Crystalline Note for the QW a near lattice matchedor strained (Ge_(1−x)(Si_(0.8)Sn_(0.2))_(z) to GaAs may be used, withtunable band gaps based on the z value. For the QDs a high Sn % GeSiSnlayer would be used. Note the dopants listed are only one of manypossible dopants, and does preclude the use of other dopants and dopingvalues are only nominal values but can take on many variations. Thethicknesses are all exemplary and can take on many different values.

The lattice constant of GaAs and Ge may be about 5.65 Å. The GeSnlattice constant can change from 5.66 Å to 5.833 Å at about 20% Sncontent, the range of lattice mismatch at the highest Sn content may beabout 3%. This makes GeSn useful for growth on Ge or GaAs or GeSiSnmaterials which may be lattice matched to Ge and GaAs, because at low Sn% GeSn can be grown coherently strained or psuedomorphic on thesematerials. For low Sn % GeSn the lattice mismatch may be reasonable andfilms can be grown pseudomorphic (strained) if thin enough, or partialrelaxation may occur for thicker films (1000 Å or more). Thus for growthof GeSn QW on Ge or GaAs or GeSiSn, planar growth can be achieved.

FIG. 39 shows the planar growth of strained GeSn 3901 (low Sn %) onGeSiSn, with GeSiSn barriers above and below the QW GeSn film. For lowSn % GeSn either Ge or GaAs barriers can be used for the formation ofthe strained GeSn QW.

The formation of quantum dot structures are a result of the ability ofself-assembled GeSn quantum dots by the Stranski-Krastanov (SK) methodthat transitions from two dimensional to island growth.

FIG. 40 shows the methodology of formation. A larger lattice constantsemiconductor is grown on a semiconductor with a smaller latticeconstant. Under proper conditions, two dimensional planar growth startsbut quickly transitions to island growth, thus forming the quantum dotstructure. The lattice constant of GeSn may be typically greater thanthat of GeSiSn. Typically the formation of the quantum dots occurs whenthe critical thickness of the GeSn layer is exceeded. The latticemismatch should be typically greater than 2% for dot formation. Therange of lattice mismatch of GeSn to that of Ge (or GaAs or latticematched Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) approximately starts at 0% andmay go up to 3% to 4% lattice mismatch at 20% Sn in GeSn. FIG. 40 showsthe island growth of strained GeSn 4001 (high Sn %) on GeSiSn barrierlayer with the subsequent formation of the QD layer.

GeSn quantum structure provide a unique methodology to form both QW andQD in the same structure because the Sn % for becoming a direct gapsemiconductor can vary from 7%≤Sn %≤20%. GeSn may be indirect up toabout 7% Sn then may become a direct gap semiconductor with anapproximate energy bandgap of 0.585 eV and an approximate latticeconstant of about 5.725 Å. The bandgap energy typically may be reducedto about 0.25 eV at 20% Sn with a lattice constant of about 5.835 Å.Utilizing Ge or GaAs or Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) barriers whichmay have a lattice constant of about 5.65, one can calculate the latticemismatch at various compositions. The lattice mismatch between GeSn toGaAs or Ge at 7% Sn content GeSn may be about 1%. The lattice mismatchbetween GeSn (20% Sn) to GaAs or Ge or Ge_(1-x)(Si_(0.8)Sn_(0.2))_(x)may be about 3% to 4%. Typically the formation of the quantum dotsgenerally occurs when the critical thickness of the GeSn layer isexceeded. The lattice mismatch should be typically greater than 2% forquantum dot formation. A 2% lattice mismatch of GaAs to the GeSncorresponds to a lattice constant of about 5.76 Å which is about 12% Snin GeSn. Thus if one grows on Ge or GaAs orGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) barriers, one can get GeSn planar directgap Type I QW for 7% Sn % 12% and direct gap type I QD for 12% Sn % 20%.The GeSn direct gap energies may vary from 7% Sn with an approximatebandgap energy of 0.585 eV; to 12% Sn with an approximate bandgap energyof 0.48 eV; to 20% Sn with an approximate bandgap energy of about 0.25eV. Thus GeSn QW energies could be in the near-IR and the GeSn QDenergies could be in the mid-IR, utilizing the exact same laser ortransistor laser or LET structure.

Exemplary Configuration 2A: Ordered InGaP Emitter-GeSiSn Base-GaAsCollector double heterojunction transistor. The device elucidated caninclude a double heterojunction InGaP—GeSiSn—GaAs HBT device. TheGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) for z≤0.5 can be lattice matched to GaAsand InGaP at the composition In_(0.49)Ga_(0.51)P. In_(0.49)Ga_(0.51)Pcan be grown in two forms ordered and disordered. InGaP semiconductorgrown by various epitaxial growth technologies can be latticed matchedto GaAs. At high temperature growth the InGaP can grow in a crystallinestructure such that the sheets of In—P and Ga—P atoms can alternate inthe (001) planes of the face centered cubic (FCC) unit cell without theintermixing of the Ga and In atoms on the lattice planes. Such anarrangement may result in a small conduction band discontinuity betweenthe InGaP and GaAs and is called the ordered phase (this can be ofweakly type I or weakly type II because it is close to zero). Theordered phase has an approximate bandgap energy of 1.85 eV and thedisordered phase has an approximate bandgap energy of 1.9 eV, thus theordered phase has a bandgap energy of which may be 0.05 eV less than thedisordered phase. With different growth conditions, the In and Ga atomscan intermix and the disordered InGaP phase can form, which may have alarger conduction band offset of 0.1 eV (type I) vs. 0.03 eV for theordered phase. It is also possible to have a mixture of ordered anddisordered InGaP materials. The lattice constant of GaAs and Ge may beabout 5.65 Å, and this may be the lattice constant of InGaP at thecomposition In_(0.49)Ga_(0.51)P.

In some examples, the ordered phase may have an advantage to thedisordered phase, because the ordered phase may have a near zeroconduction band offset. In some examples, this device has desirable basecharacteristics with a low voltage base turn-on region and that theGeSiSn base region can be directly inserted into a standard InGaP—GaAsHBTs, which is typically used in RF power amplifiers in wireless devicesand cellular handsets to send the voice and data to the cell tower. Inan inverted HBT structure by using the ternary alloy InGaP as theemitter and varying the In composition away from the latticed matchedcondition, strain can be introduced into the GeSiSn base layer, thus theGeSiSn layer can be tensile or compressively strained, an may have atunable bandgap energy from 0.66 eV to about 1 eV.

FIG. 41 shows an exemplary flat band energy diagram of an NPN HBT withan ordered InGaP emitter, GeSiSn base, and a GaAs collector 4100. Thelattice matched Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) for z≤0.5 to GaAs may beused, with tunable band gaps based on the z from 0.66 eV to 1 eV. Thistype of HBT structure is called an asymmetric double heterojunctiondevice. Note conduction band offsets may be less than 0.1 eV and may bedesirable for NPN transistors. The ordered In_(0.49)Ga_(0.51)P 4101(disordered InGaP can also be used here) may be a good material for theemitter because it of the small conduction band offset and a largevalence band offset with GeSn 4102 P⁺ base region. The N-type GaAs 4103is a proven collector material for HBTs.

The base can be graded from GeSiSn—GeSn to have electric fieldenhancement of the charge carriers (electrons). Such structure createsan electric field that accelerates the electrons across the base to thecollector.

FIG. 42 shows an exemplary flat band energy diagram of an NPN HBT withan ordered InGaP N emitter 4200, a graded GeSiSn—GeSn 4201 P⁺ base, anda GaAs N− collector 4103, and an Ordered InGaP 4101. The compositionallygraded GeSiSn—GeSn 4201 layer can comprise at the emitter-base interfacea lattice matched or near latticed matched or strainedGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAs, where the GeSiSn may becompositionally graded by reducing the Si content and increasing Gecontent to GeSn at the collector interface. The grading range can gofrom GeSiSn at the emitter-base junction to GeSn at the base-collectorjunction at various compositions, which provides for Field Enhancement4202 of the carriers.

Table 6 shows an exemplary epitaxial structure of an NPN HBT with anordered InGaP emitter, GeSiSn base region, and a GaAs collector.

TABLE 6 Epitaxial structure of NPN HBT with ordered InGaP emitter-GeSiSnbase-GaAs collector. Layer Layer Name Description Comment 1 N⁺ Cap ~1000Å InGaAs (Te-doped >10¹⁹ cm⁻³) 2 N⁻ Emitter Cap ~1500 Å GaAs (Si-doped~5 × 10¹⁸ cm⁻³) 3 N⁻ Emitter ~500 Å In_(0.49)Ga_(0.51)P (Si-doped ~3 ×10¹⁷ cm⁻³) Ordered 4 P⁺ Base ~500 Å Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z) (forz ≤ 0.5) Latticed matched 0 < Si % ≤ 40% or 0 ≤ Sn % ≤ 10%Compositionally Thickness range 100 Å-5000 Å GeSiSn GeSiSn—GeSn 5 N⁻Collector ~10000 Å GaAs (Si-doped ~1 × 10¹⁶ cm⁻³) 6 N⁺ Sub-Collector~5000 Å GaAs (Si-doped ~5 × 10¹⁸ cm³) 7 High Purity Buffer ~500 Å GaAs(un-doped) UID 8 GaAs semi-insulating or conducting Substrate Note thecompositionally graded GeSiSn—GeSn layer can comprise at theemitter-base interface a lattice matched or near latticed matched orstrained Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z) to GaAs can be compositionallygraded for the GeSiSn by reducing the Si % and increasing Ge % to GeSnat the collector interface. The grading range can go from GeSiSn at theemitter-base junction to GeSn at the base-collector junction at variouscompositions. Note the dopants listed are only one of many possibledopants, and does preclude the use of other dopants and doping valuesare only nominal values but can take on many variations. The thicknessesare all exemplary and can take on many different values.

It should be noted that there are many types of N-type and P-typedopants. For standard III-V semiconductors like GaAs, InP, InGaAs,InGaP, the N-type dopants may be Si, Ge, Sn, Pb, S, Se, Te. The P-typedopants for standard III-V semiconductors may be C, Zn, Be, Mg. Commondopants for group IV semiconductors like GeSn, Ge, Si, SiGe, GeSiSn forN-type dopants may be P, As, Sb. The P-type dopants may be B, Al, Ga.

GeSiSn used as a base material in HBTs has many advantages. At low Sn %GeSiSn latticed matched to GaAs has the following properties that makeit an excellent P-type base. GeSiSn has a low bandgap (the term lowenergy bandgap base typically refers to the relevant semiconductors withbandgaps less than 1.0 eV, like GeSn or Ge or GeSi, or GeSiSn or InGaAsor GaAsSb) which results in a low turn-on voltage. The GeSiSn holemobility is high and acceptors can be incorporated to high density(>1×10¹⁹ cm⁻³), thus the base can be made ultra-thin (less than 5000 Å)while maintaining a low base sheet resistance which increases currentgain and decreases electron transit time. GeSiSn may have shallowacceptors, so that the hole concentration is generally equal to theacceptor doping level and independent of temperature. The surfacerecombination velocity is low for P-type Ge. Low resistance ohmiccontacts can be formed on P-type GeSiSn. GeSiSn mobility (electron andhole) can be significantly improved by being biaxially tensile strain,thus for both NPN and PNP structures the base sheet resistance can beimproved significantly.

Typically for HBTs the collector is grown first followed by growing thebase and then growing the emitter. However, for this structure, it canbe advantageous to grow an inverted HBT. By growing theIn_(0.49)Ga_(0.51)P emitter first, one could increase the indium contentto greater than 49% In, thus, the bandgap energy would be reduced, butthe lattice constant would be increased. The conduction band offsetbetween the InGaP (In %>49) would cause the bands to be closer to zerooffset between the InGaP and Ge. This methodology could be applied to aGeSiSn base.

FIG. 43 shows an exemplary flat band energy diagram of an inverted NPNHBT structure where the emitter is grown first, and the base material isstrained GeSiSn. This Inverted HBT structure emitter grown firstcollector up 4300 has a field enhancement region 4303 in thecompositionally graded InGaP 4301 N⁻ emitter. This structure allows forthe P⁺ base to be strained GeSiSn 4302, thus possibly enhancing the holemobility. One could decrease the In % in the InGaP and then the GeSiSnwould be biaxially compressively strained.

The device structure advantages: By growing the emitter InGaP on GaAs,one can initially lattice match the InGaP to the GaAs. When the Incomposition can be increased to the point where GeSiSn is biaxiallytensile strained to may be about 2% it then may become a direct gapsemiconductor.

Tensile Strain effects on GeSiSn: It has shown that biaxial tensilecompression may cause enhancements in the hole and electron mobility.Biaxial tension on the band structure of GeSiSn breaks the heavy holeand light hole band degeneracy and raises the light hole above the heavyhole band. This effectively increases may increase the hole mobility.Typically the for low Sn % GeSiSn which may be latticed matched to GaAsthe band structure shows that it is an indirect semiconductor becausethe “L” point <111> is the conduction band minimum and the gamma “

” point is the valence band maximum. However GeSiSn may become a directgap semiconductor with 1.4% biaxial tensile strain or greater, becausethe gamma “

” point in GeSiSn band structure gets closer to the valence band maximumfaster than the “L” point <111>, thus making it a direct bandgapsemiconductor.

With biaxial tensile strain there may be a dramatic increase in theGeSiSn hole mobility “μ_(h)”. Thus, by growing an inverted emitterstructure one can effectively tensile or compressive strain the GeSiSnlayer. For example it has been shown experimentally that biaxial tensilecan increase the in-plane hole mobility at 3% biaxial strain of a Gehole mobility >40,000 cm²/Vs. If the InGaP is graded to higher In % thenan electric field can be built-in that can promote free charge carriersfrom the emitter into the base region.

Compressive strain effects on GeSiSn: GeSiSn under biaxial compressionmay show enhancements in the in-plane hole mobility. It has been shownexperimentally that biaxial compressive strain of 1.7% in the Ge layerincreases the low field hole mobility by a factor of 3.38 to 6350cm²/V-s.

The elucidated tensile and compressive strain effects should also workfor GeSiSn for low compositions of Sn %.

FIG. 44 shows an exemplary flat band energy diagram showing an invertedtensile strained GeSi HBT structure emitter grown first collector up4400. This NPN HBT structure where the emitter is grown first, and thebase material may be tensile strained GeSi 4402 may have someadvantages. This inverted HBT structure has a field enhancement region4303 in the graded InGaP 4301 N⁻ emitter. This structure allows for theP⁺ base to be tensile strained GeSi 4402, thus possibly enhancing thehole mobility. By utilizing InGaP in this configuration one can strainthe GeSi in tension or compression.

If an inverted structure is not desirable, the collector grown firststructure (emitter up) can be grown and the InGaP collector can begraded as follows: from the GaAs sub-collector the InGaP starts at 49%In, then is slowly graded up to an In % greater than 49% at the start ofthe GeSiSn base region. This results in field enhancement region in thecollector to accelerate the electrons to the sub-collector.

FIG. 45 shows an exemplary flat band energy diagram of an NPNconfiguration, compressively strained GeSiSn HBT collector grown firstemitter up 4500 structure, where the compressive strained GeSiSn 4501 isgrown on the N⁻ collector InGaP 4502 compositionally graded from In 49%to >49% collector which now has a field enhancement region 4503. Thisdevice has the advantage that it is a true double heterojunction almostsymmetric device. This may minimize the offset voltage found in standardInGaP—GaAs HBTs that causes a reduction in power added efficiency.

A variation of this device results in GeSiSn that may or may not bebiaxially strained, by having both the emitter and collector InGaPlayers compositionally graded. Basically this is a combination of thepreviously described embodiments for the strained GeSiSn HBTs. Here theemitter and collector both have field enhancement regions because theInGaP is graded in both layers. The standard configuration where thecollector is grown first (emitter up) and the InGaP collector can begraded as follows: from the GaAs sub-collector the InGaP starts at 49%In, then is slowly graded up to an In % greater than 49% at the start ofthe GeSiSn base. This process is repeated for the emitter where InGaPstarts at 49% In, then is slowly graded up to an In % greater than 49%at the start of N emitter contact region.

FIG. 46 shows an exemplary flat band energy diagram of a GeSiSn DoubleHBT Structure graded Emitter and graded Collector grown first 4600,where the GeSiSn 4605 base may or may not be compressively strained. TheN⁻ emitter InGaP 4601 is graded from In % 49% to >49% has a fieldenhancement region 4602. The N⁻ collector InGaP 4603 is graded from In %49% to <49% has a field enhancement region 4604. The field enhancementregions cause an acceleration of the electrons to the NPN device, thusreducing the transit time of the device.

Note through this patent InGaP is used throughout the text. Whereordered InGaP is referred to an equivalent device using disordered InGaPcan be used. Likewise where disordered InGaP is used ordered InGaP canalso be used. Though at some instance the lattice matched composition toGaAs is used In_(0.49)Ga_(0.51)P. Though this is a useful “In”composition for starting the InGaP layer, it can be graded or have adifferent composition.

Exemplary Configuration 2B: NPN Disordered InGaP Emitter-GeSiSnBase-GaAs Collector double heterojunction transistor: The deviceelucidated can include a double heterojunction disorderedIn_(0.49)Ga_(0.51)P—GeSiSn—GaAs HBT device. In some examples, thisdevice has desirable base characteristics with a low voltage baseturn-on region. This device structure can be directly inserted intostandard manufacturing InGaP—GaAs HBT. This is a slight variation onConfiguration 2A. The difference is the conduction band offset ofdisordered InGaP to GeSiSn may be <0.2 eV and the valence band offset ofthe disordered InGaP to GeSn (low Sn %) may be >0.8 eV. In someinstances it can be easier to grow the disordered InGaP.

Exemplary Configuration 2C: NPN AlGaAs Emitter-GeSiSn Base-GaAsCollector double heterojunction transistor: The device elucidated caninclude a double heterojunction AlGaAs—GeSiSn—GaAs HBT device. Thelattice matched Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) for z≤0.5 to GaAs caneasily be tensile strained by changing the ratio of Si/Sn to less than4. Like wise the lattice matched Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAscan be compressively strained by changing the ratio of Si/Sn to greaterthan 4. The previous embodiments have elucidated the advantages oftensile strained GeSiSn or compressively strained GeSiSn. In someexamples, this device has desirable base characteristics with a lowvoltage base turn-on region. This is a second variation on Configuration2A. For AlGaAs for Al % less than 0.4 the material is direct gapsemiconductor. For example the energy bandgap of Al_(0.3)Ga_(0.7)As maybe 1.8 eV as opposed In_(0.49)Ga_(0.51)P, which has an energy bandgap of1.85 eV.

FIG. 47 shows an exemplary flat band energy diagram of the NPN AlGaAsEmitter-GeSiSn Base-GaAs Collector double HBT 4700. In this HBT the Nemitter is Al_(0.3)Ga_(0.7)As 4701 but the Al % could be varied todifferent levels for possibly enhanced carrier transport.

To fabricate a light emitting NPN heterojunction bipolar transistor inthis Al_(0.3)Ga_(0.7)As (InGaP could also be used as the emitter andcollector) emitter HBT, a GeSn QW or QD region can be inserted into theGeSiSn base (GaAs could also be used as the base).

FIG. 48 shows an exemplary flat band energy diagram of the NPN HBT laserwith AlGaAs emitter/cladding and AlGaAs collector/cladding 4800. This isan exceptional device because the type I alignment allows for excellentcarrier and optical confinement. The device structure is symmetric. TheN⁻ Al_(0.3)Ga_(0.7)As 4801 & 4805 is an excellent cladding layer and hassmall mismatch with GaAs. The P⁺ GeSiSn base 4802 & 4804 acts as thebarrier layer for the GeSn QW or QD 4803 active region. The large energybandgap difference between the N⁻ Al_(0.3)Ga_(0.7)As 4801 & 4805 and theP⁺ GeSiSn base 4802 & 4804 ensures a large index of refractiondifference at the N⁻ emitter/cladding 4807 and P⁺ GeSiSn 4802 baseinterface; and a large index refraction difference at the P⁺ GeSiSn base4804 and N⁻ collector/cladding 4808, thus making an excellent waveguide4806 to optically confine the light produced by the active region. Thelaser can require a resonant cavity to get optical gain, and typicallythis can formed from the front and back cleaved facets of thesemiconductor crystal wafer.

Table 7 shows an exemplary table of the epitaxial structure of an NPNlight emitting AlGaAs—GeSiSn—GeSn—GeSiSn—AlGaAs HBT.

TABLE 7 An exemplary epitaxial structure of an NPN edge emittingtransistor laser structure with a GeSn QW or QD active region in a GaAsP-type base/barrier material and AlGaAs Cladding. Layer Layer NameDescription Comment 1 N⁺ Cap ~1000 Å InGaAs (Te-doped >10¹⁹ cm⁻³) 2 N⁻Emitter/Cladding ~5000 Å Al_(0.3)Ga_(0.7)As (Si-doped ~3 × 10¹⁷ cm⁻³)Different A % AlGaAs can be used 3 P⁺ Base/Barrier ~500 Å GeSiSn(B-doped >10¹⁹ cm⁻³) 4 QW ~55 Å GeSn For light emission or QD QW (Sn %~0% to 10% GeSn) 1000 nm-5000 nm QW thickness range 10 Å-1000 Å QD (Sn %~10% to 20% GeSn) QD size range 10 Å-200 Å 5 P⁺ Base/Barrier ~500 ÅGeSiSn (B-doped >10¹⁹ cm⁻³) 6 N⁻ Collector/Cladding ~5000 ÅAl_(0.3)Ga_(0.7)As (Si-doped ~3 × 10¹⁷ cm⁻³) Different A % AlGaAs can beused 7 N⁺ Sub-Collector ~500 Å GaAs (Si-doped ~5 × 10¹⁸ cm⁻³) 8 N⁺Buffer ~500 Å GaAs (Si-doped ~5 × 10¹⁸ cm⁻³) 9 N⁺ GaAs conductingsubstrate Crystalline Note the barriers are lattice matched orcoherently strained Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z) to GaAs for z ≤ 0.5.Note the dopants listed are only one of many possible dopants, and doespreclude the use of other dopants and doping values are only nominalvalues but can take on many variations. The thicknesses are allexemplary and can take on many different values.

Exemplary Configuration 3: An NPN and PNP GeSiSn Emitter-GeSnBase-GeSiSn Collector symmetric double heterojunction transistor. Thisdevice configuration is different because GeSiSn can be latticed matchto GeSn, even though the GeSiSn may have a larger bandgap energy thanGeSn. Because the ternary alloy GeSiSn can be grown at variouscompositions, it is possible to also biaxial tensile strain orcompressive strain the GeSn base region. For GeSiSn the Sn % and Si %can be adjusted so that the lattice parameter remains constant. AlsoP-type and N-type doping have been achieved in GeSiSn. GeSiSn can begrown on Si, GaAs, Ge substrates. For exemplary Configuration 3, Sisubstrates is a possible choice.

For Si based HBTs, GeSiSn is a unique semiconductor alloy because it canbe latticed matched to Ge or GaAs at the compositionGe_(1-z)(Si_(0.8)Sn_(0.2))_(z), where z can vary from 0 to 0.5 and thedirect gap energy of this material can vary from 0.66 eV to 1.1 eV. ThusGeSiSn is an excellent emitter for a Si HBT or a barrier layer for a Gequantum well or quantum dot (for GeSn quantum well or quantum dot),because it can be latticed matched to Ge or can compressively strain theGe thus promoting island growth necessary for quantum dot formation. Bylowering the Si to Sn ratio in GeSiSn the lattice constant can bedecreased. The GeSiSn can also be latticed matched to GeSn or cantensile strain or compressively strain the GeSn layer.

FIG. 49 shows a possible exemplary flat band energy band diagram for asymmetric double HBT GeSiSn emitter-Ge base-GeSiSn collector structure4900 which can work as an NPN or PNP transistor device. Note that a GeSnlayer can be used as the base with similar results. However, becauseGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) 4901 & 4903 can be grown at differentalloy (z) compositions, both compressive and tensile strain can beapplied to the Ge 4902 base, both configurations PNP and NPN are useful.This figure shows the flat “

” band edge energy diagram of the material structure.

The base can be graded from GeSiSn to GeSn to have electric fieldenhancement of the charge carriers (electrons and holes) as shown in the“r” band edge diagram of FIG. 50.

FIG. 50 shows a possible exemplary flat band energy band diagram forGeSiSn emitter-graded Ge—GeSn base-GeSiSn collector structure double HBT5000 which can work as an NPN or PNP transistor device. With the gradedGeSiSn—GeSn 5001 base region a field enhancement region 5002 is createdin the base. Starting with an emitter Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z)4901 (near latticed matched to Ge) at the emitter-base interface andthen a compositionally graded GeSiSn—GeSn 5001 layer which can becomprised of GeSiSn compositionally graded by reducing the Si contentand increasing Ge content to GeSn at the collector interface 4903. Thegrading range can go from GeSiSn at the emitter-base junction to GeSn atthe base-collector junction at various compositions.

Table 8 shows a possible exemplary structure for a symmetric doubleheterojunction GeSiSn emitter-Ge base-GeSiSn collector structure whichcan work as an NPN device grown on a Si substrate. If the GeSiSn latticeconstant is made larger than the Ge lattice constant, the Ge can betensile strained. This may cause the light hole band to rise above theheavy hold band in the valence band and may result in a significantenhancement in the P-type Ge base mobility and, thus, the same basethickness the base sheet resistance can be reduced and the highfrequency performance of the transistor is (F_(max)) increased. Becausethe hole mobility may be enhanced, the base resistivity may be reduced.A thinner base may promote an F_(T) to increase. In this exemplarystructure the base could be a P⁺ GeSn layer.

TABLE 8 Epitaxial structure of an NPN heterojunction GeSiSn emitter-Gebase-GeSiSn collector. Layer Layer Name Description Comment 1 N⁺ EmitterCap ~1500 Å SiGe (As-doped ~5 × 10¹⁸ cm⁻³) 2 N⁻ Emitter ~500 ÅGe_(1−z)(Si_(0.8)Sn_(0.2))_(z) (As-doped ~3 × 10¹⁷ cm⁻³) 3 P⁺ Base ~500Å Ge (B-doped >10¹⁹ cm⁻³) Or can be graded Or GeSn, Sn content 0 ≤ Sn %≤ 20% Ge—GeSn for field Thickness range 100 Å-5000 Å enhancement 4 N⁻Collector ~10000 Å Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z) (As-doped ~1 × 10¹⁶cm⁻³) 5 N⁺ Sub-Collector ~5000 Å SiGe (As-doped 5 × 10¹⁸ cm⁻³) SiGe Gecontent can be varied to accomodate the Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z)layer 6 N⁺ Buffer ~500 Å Si (As-doped 2 × 10¹⁸ cm⁻³) 7 N⁺ Si substrateCrystalline Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z) for z ≤0.5 can be latticedmatched to Ge. Note the dopants listed are only one of many possibledopants, and does preclude the use of other dopants and doping valuesare only nominal values but can take on many variations. The thicknessesare all exemplary and can take on many different values.

Table 9 shows a possible exemplary structure for a symmetric doubleheterojunction GeSiSn emitter-Ge base-GeSiSn collector structure whichcan work as a PNP device. If the GeSiSn lattice constant is made largerthan the Ge lattice constant then the Ge can be tensile strained. Thiscauses the light hole band in the valence to split from the heavy holeband and results in an enhancement in the P-type Ge base mobility, thusreducing the base sheet resistance and increasing the high frequencyperformance of the transistor. In this exemplary structure the basecould be a heavily N⁺ GeSn layer.

TABLE 9 Epitaxial structure of a PNP heterojunction GeSiSn emitter-Gebase-GeSiSn collector. Layer Layer Name Description Comment 1 P⁺ EmitterCap ~1500 Å SiGe (B-doped ~5 × 10¹⁸ cm⁻³) 2 P⁻ Emitter ~500 ÅGe_(1−z)(Si_(0.8)Sn_(0.2))_(z) (B-doped ~3 × 10¹⁷ cm⁻³) 3 N⁺ Base ~500 ÅGe (As-doped >10¹⁹ cm⁻³) Or can be graded Or GeSn, Sn content 0 ≤ Sn % ≤20% Ge—GeSn for field Thickness range 100 Å-5000 Å enhancement 4 P⁻Collector ~10000 Å Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z) (B-doped ~1 × 10¹⁶cm⁻³) 5 P⁺ Sub-Collector ~5000 Å SiGe (B-doped ~5 × 10¹⁸ cm⁻³) SiGe Gecontent can be varied to accomodate the Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z)layer 6 P⁺ Buffer ~500 Å Si (B-doped ~2 × 10¹⁸ cm⁻³) 7 P⁺ Si substrateCrystalline Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z) for z ≤ 0.5 can be latticedmatched or near latticed matched to Ge. GeSiSn can also be near latticedmatched to GeSn. Note the dopants listed are only one of many possibledopants, and does preclude the use of other dopants and doping valuesare only nominal values but can take on many variations. The thicknessesare all exemplary and can take on many different values.

FIG. 51 shows a possible exemplary flat band energy band diagram for asymmetric double heterojunction light emitting transistor or transistorlaser where a Ge QW or QD is embedded in the GeSiSn base region withSiGe emitter/cladding and SiGe collector/cladding forming the lightemitting HBT 5100. Note a GeSn QW or QD can also be used here. Thisstructure can work as an NPN or PNP transistor light emitter device.Here a Ge QW or QD 5103 is inserted into aGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) 5102 & 5104 base region. Note a GeSn QWor QD can replace the Ge QW or QD. The SiGe 5101 emitter/cladding andthe SiGe 5105 collector/cladding, form the major index difference forlight confinement in the waveguide 5106 region, and also have a largebandgap energy to funnel carriers into the active region.

Table 10 shows a possible exemplary structure for a symmetric NPN doubleheterojunction transistor laser or light emitting transistor structurewith an N⁻ SiGe emitter/cladding, a Ge QW or QD embedded in P⁺ GeSiSnbase with an N⁻ SiGe collector/cladding. Note a GeSn QW or QD canreplace the Ge QW or QD.

TABLE 10 A symmetric NPN double heterojunction transistor laser or lightemitting transistor structure with a SiGe emitter/cladding, a Ge QW orQD embedded in GeSiSn base with a SiGe collector/cladding. Layer LayerName Description Comment 1 N⁺ Cap ~1000 Å SiGe (As-doped >10¹⁹ cm⁻³) 2N⁻ Emitter Cladding ~4000 Å SiGe (As-doped ~5 × 10¹⁷) 3 P⁺ Base ~500 ÅGe_(1−z)(Si_(0.8)Sn_(0.2))_(z) (B-doped >10¹⁹ cm⁻³) 4 QW ~55 Å Ge Lightemission or QD or 1000 nm-5000 nm. GeSn GeSn QW or QD QW (Sn % ~0% to10% GeSn) can be used here. QW thickness range 10 Å-1000 Å QD (Sn % ~10%to 20% GeSn) QD size range 10 Å-500 Å 5 P⁺ Base ~500 ÅGe_(1−z)(Si_(0.8)Sn_(0.2))_(z) (B-doped >10¹⁹ cm⁻³) 6 N⁻Collector/Cladding ~4000 Å SiGe (As-doped ~5 × 10¹⁷ cm⁻³) 7 N⁺sub-collector ~500 Å Si (As-doped ~5 × 10¹⁸ cm⁻³) 8 N⁺ Si conductingsubstrate Crystalline

Table 11 shows a possible exemplary structure for a symmetric PNP doubleheterojunction transistor laser structure or light emitting transistorwith a P⁻ SiGe emitter/cladding, Ge QW or QD embedded in N⁺ GeSiSn basewith a P⁻ SiGe collector/cladding. Note a GeSn QW or QD can replace theGe QD or QW.

TABLE 11 A symmetric PNP double heterojunction transistor laser SiGeemitter/cladding, Ge QW or QD embedded in GeSiSn base, and SiGecollector/cladding. Layer Layer Name Description Comment 1 P⁺ Cap ~1000Å SiGe (B-doped >10¹⁹ cm⁻³) 2 P⁻ upper Cladding ~4000 Å GaAs (B-doped ~5× 10¹⁷) 3 N⁺ Base ~500 Å Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z) (As-doped >10¹⁹cm⁻³) 4 QW ~55 Å Ge Light emission or QD or 1000 nm-5000 nm. GeSn GeSnQW or QD QW (Sn % ~0% to 10% GeSn) can be used here. QW thickness range10 Å-1000 Å QD (Sn % ~10% to 20% GeSn) QD size range 10 Å-500 Å 5 N⁺Base ~500 Å Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z) (As-doped >10¹⁹ cm⁻³) 6 P⁻Collector/Cladding ~4000 Å SiGe (B-doped ~5 × 10¹⁷ cm⁻³) 7 P⁺Sub-collector ~500 Å Si (B-doped ~5 × 10¹⁸ cm⁻³) 8 P⁺ Si substrateCrystalline

It should be noted that there are many types of N-type and P-typedopants. For standard III-V semiconductors like GaAs, InP, InGaAs,InGaP, the N-type dopants may be Si, Ge, Sn, Pb, S, Se, Te. The P-typedopants for standard III-V semiconductors may be C, Zn, Be, Mg. Commondopants for group IV semiconductors like GeSn, Ge, Si, SiGe, GeSiSn forN-type dopants may be P, As, Sb. The P-type dopants may be B, Al, Ga.

Exemplary Configuration 4: Si Emitter-SiGe base with Ge QD or QW-SiCollector transistor laser. The introduction of a Ge QD or QW or (GeSnQD or QW) into a standard SiGe HBT design allows for the noveldevelopment of a Si photonic transistor laser. SiGe has a wide range ofbandgaps from a starting point of Si with a bandgap energy of 1.1 eV, atSi_(0.8)Ge_(0.2) has a bandgap energy of approximately 1 eV, atSi_(0.6)Ge_(0.4) has a bandgap energy of approximately 0.93 eV, and atSi_(0.2)Ge_(0.8) has a bandgap energy of approximately 0.87 eV. Tofabricate a light emitting bipolar transistor the flat band diagram isshown in FIG. 52 for an NPN device. Inserted into the SiGe base is a GeQD or QW or (or GeSn QD or QW).

FIG. 52 shows an exemplary flat band energy diagram of a Si Emitter-SiGebase with GeSi QD or QW-Si Collector light emitting HBT 5200. This HBTlaser is grown on Si substrates, thus compatible with Si processing.Here a GeSi (low Si %<20%) QD or QW 5204 has barriers region ofSi_(0.6)Ge_(0.4) 5203 & 5205 P⁺ base/barrier. The Si_(0.6)Ge_(0.4) (hasan approximate band gap energy of 0.93, but other compositions of SiGecan be used) forms the P⁺ base and also acts as a barrier layer forquantum confine the electrons and holes in the GeSi QD or QW 5204. For aQD the growth of a large lattice constant material on a smaller latticeconstant material results in strained layer epitaxy allowing theself-assembled three dimensional island growth. Typical quantum dotdiameters are in the range of 1-20 nm, but are dependent on thewavelength of light that needs to be emitted. For a growth of the QW, itis typically grown on a latticed match layer with a larger bandgap layerthan the QW material or can be grown strained. A large bandgap barrierthen covers the QW layer. Typical QW thicknesses are in the range of5-20 nm, but are not restricted to these thicknesses. The GeSi QD 5204inserted into a base/barrier serves for the collection region forelectrons and holes to recombine to generate light. The Si_(0.6)Ge_(0.4)5203 & 5205 also serve as the optical confinement layer and thewaveguide material. The Si 5202 & 5206 serves as the N⁻ emitter/claddingand N⁻ collector/cladding material for this structure. The claddingserves as funneling carriers into the active/waveguide region and trapsthe emit light in the waveguide 5207 structure. GeSiSn could also beused as the QD active region.

FIG. 53 shows a possible cross-sectional device depiction of a Si basededge emitting transistor laser or light emitting structure 5300. Thetransistor laser includes a GeSi QD 5304 (or a GeSiSn QD can also beused) inserted into a Si_(0.8)Ge_(0.2) 5303 & 5305 P⁺ base/barrier ofthe HBT. Layer 5301 is the highly conductive N⁺ type Si contact. Thelaser can require a resonant cavity to get optical gain, and typicallythis can be formed from the front and back cleaved facets of thesemiconductor crystal wafer. The structure can be grown on N⁺ Siconducting substrate 5308, which is the seed crystal to grow the fullstructure. An N⁺ Si sub-collector 5307 is grown on the substrate. An N⁻Si collector/cladding 5306 and the N⁻ Si emitter/cladding 5302 do dualfunctions of optical confinement of the light 5309 produced from theactive region GeSi QD 5304 and the controlling the flow of electrons andholes. The P⁺ Si_(0.8)Ge_(0.2) Base 5305 & 5303 form the barriermaterial for the GeSi QD 5304, and also provide the waveguide material.The laser can require a resonant cavity to get optical gain, andtypically this can be formed from the front cleaved facets 5311 and backcleaved facets 5310 of the semiconductor crystalline structure.

Table 12 shows an example of an exemplary structure that could be grown.Note for this HBT device the Si_(0.8)Ge_(0.2) base could be graded downto lower Si content.

TABLE 12 Epitaxial structure of NPN light emitting SiGe—GeSi—SiGe HBT.Layer Layer Name Description Comment 1 N⁺ Cap ~2000 Å Si (As-doped >10¹⁹cm⁻³) As = Arsenic 2 N⁻ Emitter/Cladding ~5000 Å Si (As-doped ~5 × 10¹⁷cm⁻³) 3 P⁺ Base ~500 Å Si_(0.8)Ge_(0.2) (B-doped >10¹⁹ cm⁻³) SiGe couldbe graded 4 QD GeSi Light emission Si % ≤20% 1000 nm-5000 nm. QD sizerange ~10 Å-500 Å GeSiSn QD can be QW thickness range ~10 Å-1000 Å usedhere. 5 P⁺ Base ~500 Å Si_(0.8)Ge_(0.2) (B-doped >10¹⁹ cm⁻³) SiGe couldbe graded 6 N⁻ Collector/Cladding ~5000 Å Si (As-doped ~5 × 10¹⁷ cm⁻³) 7N⁺ Sub-Collector ~2000 Å Si (As-doped ~5 × 10¹⁸ cm⁻³) 8 N⁺ Si conductingsubstrate Crystalline Note the dopants listed are only one of manypossible dopants, and does preclude the use of other dopants and dopingvalues are only nominal values but can take on many variations. Thethicknesses are all exemplary and can take on many different values.

FIG. 54 shows a laser structure, a variation of FIG. 52, because usinghigher Ge content in the Si_(0.8)Ge_(0.4), it can be possible to produceQDs or QWs with longer wavelength light emission. FIG. 54 shows theexemplary flat band energy diagram of this structure. The laser includesa GeSi QD or QW 5404 inserted into a Si_(0.8)Ge_(0.4) P⁺ barrier/base5403 & 5405. This HBT laser is grown on Si substrates, thus compatiblewith Si processing. The Si_(0.8)Ge_(0.4) forms the P⁺ base and also actsas a barrier layer for quantum confinement of the electrons and holes inthe GeSi QD or QW. The GeSi QD or QW 5404 inserted into a base/barrierserves for the collection region for electrons and holes to recombine togenerate light. The Si_(0.8)Ge_(0.4) 5403 & 5405 also serve as theoptical confinement layer and the waveguide material. TheSi_(0.8)Ge_(0.2) 5402 & 5406 serves as the emitter/cladding andcollector/cladding material for this structure. The cladding serves asfunneling carriers into the active/waveguide 5407 region and traps theemitted light in the waveguide structure. The approximate bandgapenergies are shown below the corresponding materials.

Table 13 shows an exemplary structure that could be grown which includesSi_(0.8)Ge_(0.4)P⁺ base.

TABLE 13 Epitaxial structure of NPN light emitting SiGe—GeSi—SiGe HBT(with Si₆Ge₄). Layer Layer Name Description Comment 1 N⁺ Cap ~2000 ÅSi_(0.8)Ge_(0.2) (As-doped >10¹⁹ cm⁻³) As = Arsenic 2 N⁻Emitter/Cladding ~5000 Å Si_(0.6)Ge_(0.2) (As-doped ~5 × 10¹⁷ cm⁻³) 3 P⁺Base ~500 Å Si_(0.8)Ge_(0.4) (B-doped >10¹⁹ cm⁻³) SiGe could be graded 4QD ~55 Å GeSi Light emission Or QW Si % ≤20% 1000 nm-5000 nm QWthickness range 10 Å-1000 Å GeSn QD or QW can QD size range 10 Å-200 Åbe used here 5 P⁺ Base ~500 Å Si_(0.6)Ge_(0.4) (B-doped >10¹⁹ cm⁻³) SiGecould be graded 6 N⁻ Collector/Cladding ~5000 Å Si_(0.8)Ge_(0.2)(As-doped ~5 × 10¹⁷ cm⁻³) 7 N⁺ Sub-Collector ~2000 Å Si (As-doped ~5 ×10¹⁸ cm⁻³) 8 N⁺ Si conducting substrate Crystalline Note the dopantslisted are only one of many possible dopants, and does preclude the useof other dopants and doping values are only nominal values but can takeon many variations. The thicknesses are all exemplary and can take onmany different values.

The transistor laser has the integrated features of both the transistorand the laser. From such a structure it can be straightforward tosimplify the structure and grow a separate confinement heterostructure(SCH) laser.

FIG. 55 shows an exemplary flat band energy diagram of an SCH laserutilizing 5500 a GeSi QW or QD region 5503 located in UIDGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) barrier/OCL layer 5502 & 5504 region withP⁺ SiGe 5501 cladding and N⁺ SiGe 5505 cladding layers. This structurerepresents a PN junction or diode with an unintentionally doped (UID)active region and optical confinement region between the P⁺ SiGe 5501and N⁺ SiGe 5505 cladding. The UID Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) 5502 &5504 forms the barrier material for the GeSi QW or QD 5503 activeregion. The combination of the barrier and active region forms thewaveguide 5506 of the laser. The P⁺ SiGe 5501 cladding region serves forinjection of the holes and for the optical confinement of the lightemitted from the active region. The N⁺ SiGe 5505 cladding region servesfor injection of the electrons and for the optical confinement of thelight emitted from the active region in the waveguide 5506. The UIDGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) 5502 & 5504 could be replaced with a SiGebarrier layer as other examples of the SCH laser structure. A GeSn QW orQD could also be used.

Table 14 shows an exemplary epitaxial structure SCH injection diodelaser with a GeSi QW or QD region with GeSiSn barriers.

TABLE 14 Exemplary epitaxial structure SCH injection diode laser with aGe QW or QD region with GeSiSn barriers. Layer Layer Name DescriptionComment 1 P⁺ Cap ~1000 Å SiGe (B-doped >10¹⁹ cm⁻³) 2 P⁺ Cladding ~5000 ÅSiGe (B-doped ~1 × 10¹⁸) 3 UID Barrier/OCL ~500 ÅGe_(1−z)(Si_(0.8)Sn_(0.2))_(z) Also could use a Ge barrier 4 QW ~55 ÅGeSi Light emission or QD Si % ≤20% 1000 nm-5000 nm. QW thickness range10 Å-1000 Å A GeSn QW or QD QD size range 10 Å-200 Å can be used here. 5UID Barrier/OCL ~500 Å Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z) Also could use aGe barrier 6 N⁺ Cladding ~5000 Å SiGe (As-doped ~1 × 10¹⁸ cm⁻³) SiGe: Gecontent can be varied 7 N⁺ Buffer ~5000 Å Si (As-doped ~5 × 10¹⁸ cm⁻³) 8N⁺ Si conducting substrate Crystalline

Exemplary Configuration 5A: An NPN GaAs Emitter-GeSiSn Base-GaNCollector double heterojunction bipolar transistor with dissimilarmaterials. This device configuration comprises an emitter/base stack ofGaAs—GeSiSn wafer bonded to a GaN collector. This device configurationmay comprise an emitter/base stack of GaAs—GeSiSn or a emitter/basestack of GaAs—GeSi wafer bonded to a GaN collector. GaN with its highbandgap offers tremendous improvements in the breakdown voltage of theHBT. The device elucidated can include a double heterojunctionGaAs—GeSiSn—GaN HBT or a GaAs—GeSi—GaN device. The advent of devicetechnology based on GaN with its high electric field strength is a newdirection for high-power RF amplification. GaN based materials have alarge bandgap and high electron saturation velocity. The embodimentsdescribed herein demonstrate a new semiconductor transistor integratedcircuit with ultra-high performance in applications requiring both highspeed and high power rugged electronics. In examples described herein,the GaN can be grown on the various substrates like sapphire, SiC, SiGaAs, GaN, and template substrates.

Polar GaN wurtzite structure can be grown on sapphire, SiC (manypolytypes: 3C, 4H, 6H, etc.), Si substrates, or template substrates andhas piezoelectric and polarization charge. GaN grown in the wurtzite(hexagonal) phase results in large spontaneous and piezoelectricpolarization charge.

Non-polar GaN cubic (FCC) structure can be grown on GaAs, Si, ortemplate substrates. GaN in this form has no polarization charge. Acubic form of GaN with (001) orientation can be grown on zinc blendGaAs. Thus the cubic GaN can be grown on conducting GaAs which can actas the sub-collector. The zinc-blend (cubic) GaN collector has anegligible conduction band offset with respect to the GeSn base. Theconduction band offset between GaAs and cubic GaN may be ΔE_(C)<0.1 eV.Thus for low Sn % GeSiSn and low Si % GeSi have properties close to Ge,and the conduction band offset to GaN may be about ΔE_(C)<0.1 eV at thebase/collector heterojunction. Non-polar wurtzite forms can be cut fromthe c-plane growth along the “a” or “m” plane directions. If the GaN isgrown along the “m” or “a” plane axis, these polarization effects can beeliminated. Typical GaN wurzite crystals grown along the direction(c-plane) of III-nitrides suffer from polarization induced electricfields. Electric fields do not exist across the along nonpolardirections (a-plane or m-plane). Thus, high quality non-polar GaNsubstrate crystals are produced by slicing a c-plane GaN boule along the“a” or “m” plane. Such a material in low defect density non-polarsubstrates have improved substrates for fabrication of devices.

The GaAs—GeSiSn—GaN the heterojunction transistor described herein mayrepresent a high power and high frequency performance device. Thisdevice embodies enormous RF power output, ruggedness, high bandwidth,and good linearity, combined with low turn-on voltage, which may bedesirable for minimizing power consumption. This unique arrangement ofmaterials combines the high transconductance of heterojunction bipolartransistor (HBT) technology, with the breakdown voltage (using a GaNcollector), and a desirable emitter-base heterojunction (wide bandgapGaAs emitter on a narrow bandgap high conductivity P-type GeSiSn base).The large breakdown field of GaN may allow the use of short collectordevices with high bandwidths (e.g. cut-off frequency F_(t) and maximumoscillation frequency F_(max) >than 150 Ghz). The combination of a lowbandgap (<1.0 eV) GeSiSn base coupled with a wide bandgap GaN 9˜3.4 eV)collector can be used for high speed power applications. By using avertical stack of junctions, the device layers may be shorter, resultingin lower resistances and shorter transit delays, both contributing tomuch higher frequencies. The use of efficient GaAs—GeSiSn—GaNtransistors can significantly enhance battery life while also enablingoperation at high powers with exceptional frequency response.

The various crystal growth technologies, pulse laser ablation epitaxy,molecular beam epitaxy, metal organic chemical vapor deposition, liquidphase epitaxy, vapor phase epitaxy, or various other epitaxial growthtechniques for the growth of base-emitter stack of P⁺ GeSiSn base ontothe N⁻ GaAs emitter may be useful in devices. The baseGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) with tunable band gaps may be latticedmatched to GaAs. Also for the approximate composition the base materialGe_(0.98) Si_(0.02) may be also latticed matched to GaAs. TheGaAs—GeSiSn emitter base stack can be coupled together through waferbonding technology to the GaN collector, thus forming a monolithicGaAs(emitter)-GeSiSn(base)-GaN(collector) semiconductor stack that is adesirable HBT embodiment for high-power, high-frequency electronics canbe created. In some examples, the uniqueness of embodiments can resultin a small conduction band offset through the three differentsemiconductor materials (GaAs—GeSiSn—GaN). New materials are required tobuild high power electronics that can also operate at frequencies in the10 to 100 GHz range. The formation of lattice-matched GeSiSn on GaAsthen wafer bonded to GaN is a possible key to the realization of thesedevices.

FIG. 56 shows the energy bandgaps of various semiconductors vs. theirlattice constant. The graph has a vertical axis with the values of thebandgap energy (eV) and a horizontal axis with the values of the Latticeconstant (Å). Various semiconductors are plotted as a function of theirbandgap energy and lattice constant. The condition of lattice matchingconstrains certain combinations of semiconductors. It is readily seenthat new types of semiconductor devices can be formed if the latticematching constraint were eliminated. It would then be possible tofabricate new types of heterojunctions based on the materialscharacteristics instead of those constrained to near lattice constantmaterials.

The merging of the GeSiSn base region with the GaN collector byutilizing the wafer bonding process for fabrication of heterogeneousmaterials described herein. With this approach, the GeSiSn and GaNepitaxial layers can be joined to make a single composite structure.Monolithic wafer bonding is an advanced process for forming PNjunctions. This wafer bonding technique allows formation of a robustmonolithic structure, where the interface is covalently bonded. The newcomposite material establishes the GeSiSn—GaN base-collectorheterointerface. One could use latticed matched or near latticed matchedGe_(0.98) Si_(0.02) to GaAs as the base layer. Wafer bonding allows forthe formation of a heterointerface without having to performheteroepitaxy of two poorly latticed matched materials.

The new HBT has a base-collector junction comprising the GeSiSn P⁺ baseregion wafer bonded to the GaN N⁻ collector is described herein.Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) for z≤0.5 and Ge_(0.98) Si_(0.02) may belatticed matched or near latticed matched to GaAs. With this approach,the GeSiSn or GeSi and GaN epitaxial layers can be joined to make asingle composite crystalline structure. The wafer bonding techniquedescribed herein allows to form a junction that is a robust monolithicstructure, where the interface is covalently bonded.

FIG. 57 shows the exemplary wafer bonding process that enablesmonolithic joining of two dissimilar semiconductor materials. Byemploying pressure, heat, gas ambient, and time, covalently bondedcomposite structures can be developed. The new composite materialestablishes the critical GeSiSn—GaN base-collector heterointerface.Wafer bonding allows formation of a heterointerface without having toperform heteroepitaxy of two poorly matched materials. Exemplary waferbonding methodology comprises step S701 where the GeSiSn 5704 and GaN5705 semiconductors are cleaned in preparation for joining, step S702the GeSiSn 5704 and GaN 5705 are placed on each other in between thewafer bonder top plate 5706 and wafer bonder bottom plated 5707,basically the jaws of the wafer bonder, and held under heat 5709 andpressure 5708 for the requisite time and in a gas ambient, then stepS703 the final structure is a monolithic composite material with GeSiSn5704 bonded to GaN 5705. Also for example the composition Ge_(0.98)Si_(0.02) could also be used in this wafer bonded process, but is notonly limited to this composition

NPN GaAs—GeSiSn—GaN HBTs can include the following concepts: Growth oflattice matched P-type GeSiSn base on N-type GaAs emitter (GaAs/GeSiSnstack). For example GeSiSn at the following compositionGe_(0.95)Si_(0.04)Sn_(0.01) could be a possible of numerous candidatesfor the base region. Monolithic formation by wafer bonding ofGeSiSn/GaAs stack to the N-type GaN (to circumvent large latticemismatched growth). One of the advantages of the embodiments describedherein is the formation of a unique transistor semiconductor stack thatcan have a small conduction band offset between all three materials.

FIG. 58 shows an example of a possible exemplary flat band energydiagram wafer bonded NPN GaAs—GeSiSn—GaN HBT 5800. In this example acomposition of Ge_(0.95)Si_(0.04)Sn_(0.01) was used, but is not the onlycomposition that can be used. Here an emitter up emitter-base stack 5805comprising of N⁻ emitter GaAs 5802 with a P⁺ Base GeSiSn 5803. The fullmonolithic structure can be formed using an epitaxial liftoff (ELO)procedure. This emitter-base stack 5805 is wafer bonded to the N⁻collector GaN 5804 thus forming a wafer bonded junction 5801 at thebase-collector interface. Possible methodologies of wafer bonding thisemitter-base stack to the GaN is described in Exemplary ELO WaferBonding Configuration 6A and in Exemplary Inverted Wafer BondingConfiguration 6B. Note the conduction band offset ΔE_(C) may be lessthan 0.1 eV through the NPN HBT structure.

FIG. 58A shows an exemplary flat band energy diagram wafer bonded NPNGaAs—GeSi—GaN HBT 5800A. Here an emitter up emitter-base stack 5805Acomprising of N⁻ emitter GaAs 5802A grown on P⁺ Base GeSi 5803Astructure. In this example a composition of Ge_(0.98)Si_(0.02) layer maybe lattice matched to GaAs, however this is not the only compositionthat can be used. The full monolithic structure can be formed using anepitaxial liftoff (ELO) procedure. The GaAs—GeSi emitter-base stack5805A is wafer bonded to the N⁻ collector GaN 5804A thus forming a waferbonded junction 5801A at the base-collector interface. Possiblemethodologies of wafer bonding this emitter-base stack to the GaN isdescribed in Exemplary ELO Wafer Bonding Configuration 6A and inExemplary Inverted Wafer Bonding Configuration 6B. Note the conductionband offset ΔE_(C) may be less than 0.1 eV through the NPN HBTstructure.

The base can be graded from GeSiSn—GeSn to have electric fieldenhancement of the charge carriers.

FIG. 59 shows an exemplary flat band energy diagram of the NPN GaAs,compositionally graded GeSiSn—GeSn, GaN HBT 5900. Here a base upemitter-base stack 5905 comprises a P⁺ Base compositionally gradedGeSiSn—GeSn 5903 grown on an N⁻ emitter GaAs 5902 structure. Thecompositionally graded GeSiSn—GeSn 5903 layer can comprise at theemitter-base interface a lattice matched or near latticed matchedGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAs, the GeSiSn can becompositionally graded by reducing the Si content and increasing Gecontent to GeSn at the collector interface. The grading range can gofrom GeSiSn at the emitter-base junction to GeSn at the base-collectorjunction at various compositions. This emitter-base stack 5905 is thenwafer bonded with the P⁺ Base next to the N⁻ collector GaN 5804 thusforming a wafer bonded junction 5901 at the base-collector interface.Due to the compositional grading of the GeSiSn—GeSn 5903 in the P⁺ Base,there is a field enhancement region 5906 that accelerates the carrierstoward the collector. The methodology of wafer bonding this emitter-basestack is described in Exemplary Inverted Wafer Bonding Configuration 6B.Note the conduction band offset ΔE_(C) may be small through the NPN HBTstructure.

FIG. 60 shows an exemplary cross-sectional device depiction of the waferbonded GaAs—GeSiSn—GaN NPN double HBT 6000 in a mesa configuration. Notethat this is a vertical device, which is desirable for powerapplications because the lateral area can be minimized. The device isgrown on an N⁺ SiC 4H substrate 6006. The NPN HBT comprises an emitterbase stack 6001 with a wafer bond 6010 to the GaN structure 6002 to formthe monolithic device. The GaN structure 6002 can comprise a variety offorms, but for an exemplary case the GaN is grown on a SiC substrate,though a GaN, sapphire, GaAs, Si substrate could also be used. Startingwith an N⁺ SiC substrate 6006, which can be of the 3C, 4H, 6H, etc.variety, on which an N⁺ SiC buffer 6007 is grown. Then an N⁺ SiCsub-collector 6008 can be grown, onto which an N⁻ GaN collector 6009 isgrown. This finalizes the GaN structure 6002. Because the GaN is grownon 4H SiC (wurtzite or hexagonal), such a growth results in a polar GaNcollector 6009. For the emitter-base stack 6001 an ELO procedure to bedescribed in Exemplary Configuration 6A, forms the N⁺ GaAs contact6003—the N⁻ GaAs emitter 6004 and the P⁺ GeSiSn base 6005, finalizingthe emitter base stack 6001. P⁺ GeSn base 6005 layer forms the heavilydoped P-type base. GeSiSn also has a large hole mobility which is aprecondition for making the base region thin. The conduction band offsetbetween GaAs—GeSiSn may be small, thus resulting in a large valence bandoffset. The GaN can serve as the collector layer with a large breakdownvoltage for the transistor because it has a large bandgap energy of 3.4eV.

Table 15 is an exemplary Epitaxial structure of an NPN GaAs—GeSiSn—GaNwafer bonded HBT. In this structure, the GaN is grown on SiC which is atypical substrate for the growth and one of the many describedsubstrates that can be used. SiC is preferred for high power electronicsbecause it has the highest thermal conductivity between GaN, Si, GaAsand sapphire the other primary substrates for GaN. Note thecompositionally graded GeSiSn—GeSn layer can comprise at theemitter-base interface a lattice or near latticed matched or strainedGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAs, where the GeSiSn iscompositionally graded by reducing the Si % and increasing Ge content toGeSn at the collector interface. The grading range can go from GeSiSn atthe emitter-base junction to GeSn at the base-collector junction atvarious compositions.

TABLE 15 Epitaxial structure of an NPN GaAs—GeSiSn—GaN wafer bonded HBT.Layer Layer Name Description Comment 1 N⁺ Cap ~1000 Å InGaAs (Te-doped>10¹⁹ cm⁻³) 2 N⁻ Emitter Cap ~1500 Å GaAs (Si-doped ~5 × 10¹⁸ cm⁻³) 3 N⁻Emitter ~500 Å GaAs (Si-doped ~3 × 10¹⁷ cm⁻³) 4 P⁺ Base ~500 ÅGe_(1−z)(Si_(0.8)Sn_(0.2))_(z) Latticed matched can be B-doped >10¹⁹cm⁻³ or 0 < Si % ≤ 40% Can be compositionally 0 ≤ Sn % ≤ 10% gradedGeSiSn—GeSn Thickness range 100 Å-5000 Å 5 N⁻ Collector ~10000 Å GaN(N-doped ~1 × 10¹⁸ cm⁻³) Wafer bonded to above 6 N⁺ Sub-Collector ~5000Å SiC (N-doped ~5 × 10¹⁸ cm⁻³) 7 High Purity Buffer ~500 Å SiC (N-doped~5 × 10¹⁸ cm⁻³) N = nitrogen 8 N⁺ SiC (4H) conducting substrateCrystalline Note the dopants listed are only one of many possibledopants, and does preclude the use of other dopants and doping valuesare only nominal values but can take on many variations. The thicknessesare all exemplary and can take on many different values.

FIG. 61 shows another possible exemplary cross-section device depictionof the wafer bonded GaAs—GeSi—GaN/Si NPN double HBT 6100 in a mesaconfiguration. Note that this is a vertical device, which is desirablefor power applications because the lateral area can be minimized. Inthis case the device is grown on a face centered cubic (FCC) N⁺ Sisubstrate 6106. The NPN HBT comprises an emitter base stack 6001 with awafer bond 6110 to the GaN structure 6102 to form the monolithic device.The GaN structure 6102 can comprise a variety of forms, but for anexemplary case the GaN is grown on a Si substrate, though a GaN,sapphire, SiC, GaAs substrate could also be used. Starting with an N⁺ Sisubstrate 6106, which an N⁺ Si buffer 6107 is grown. Then an N⁺ Sisub-collector 6108 can be added, onto which an N⁻ GaN collector 6109 isgrown. This finalizes the GaN structure 6102. Because the GaN is grownon FCC Si (cubic) such a growth results in a non-polar GaN collector6109. An ELO procedure in Exemplary Configuration 6A, describes how theemitter-base stack 6001 is wafer bonded to the GaN collector structure.P⁺ GeSi base 6005 layer forms the heavily doped P-type base. For examplethe Ge_(0.98)Si_(0.02) layer may be lattice matched to GaAs. GeSi mayhave a large hole mobility which may be important for making the baseregion thin. The conduction band offset between GaAs—GeSi may be small,thus resulting in a large valence band offset. The GaN can serve as thecollector layer with a large breakdown voltage for the transistorbecause it has a large bandgap energy of 3.4 eV.

In some examples, formation of this monolithic composite material of anNPN GaAs—GeSiSn—GaN wafer bonded HBT can create a desirable devicearchitecture in that the conduction band offsets may be small for bothemitter-base and base-collector hetero-interfaces, and the valence bandoffset may be large at the emitter-base GaAs—GeSiSn and base-collectorGeSiSn—GaN heterojunctions. This property allows for the formation ofheterojunction transistor structure that can have large gain (largevalence band offset between GaAs and GeSiSn), low base sheet resistance(GeSiSn has high hole mobility), low turn-on voltage (GeSiSn has lowbandgap energy <1.0 eV), and large breakdown voltage (GaN has largebreakdown electric field strength and high saturated velocity), whichare desirable device metrics for next-generation electronic transistors.Electrons can easily be injected from the GaAs emitter through theGeSiSn base to the GaN collector. By adding the ability tocompositionally grade the base GeSiSn to GeSn such that the bandgapenergy of the material is gradually reduced throughout the base asdescribed in these configurations. This grading causes an electricfield, which in turn reduces the transit time, thus increasing F_(t).The GaAs—GeSiSn—GaN materials stack can be desirable for making NPN HBTsthat can outperform standard SiGe, GaAs, and InP heterojunction bipolartransistors.

Exemplary GaAs Emitter Advantages: The large valence band offset betweenGaAs emitter and GeSiSn base can stop back injection of holes into theemitter. This is desirable because the base is doped heavily P-type(typically >1×10¹⁹ cm⁻³), with such high doping of the base, theemitter-base valence band offset blocks the holes even though the basedoping is much higher than the N-type emitter doping (low 10¹⁷ cm⁻³).This allows for low N-type doping of the emitter and high P-type dopingof the base, thus lowering base emitter capacitance while stillachieving sizable current gain. Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) can belattice matched to GaAs which may enable dislocation free crystalgrowth. The use of a GaAs (instead of InGaP) emitter and GaN (instead ofGaAs) collector significantly increases the overall thermal conductivityof the material structure. The GaAs—GeSiSn emitter base junction has alarge valence due to the small conduction band discontinuity. Thiseliminates the back injection of holes to the emitter from the base,which reduces the gain of the transistor.

Exemplary GeSiSn Base Advantages (low Sn % similar properties to Ge):GeSiSn can have a low bandgap (semiconductors with bandgaps less than0.8 eV, which results in low turn-on voltage (less than 0.5 V). GeSiSn(low Sn %) hole mobility is high (2000 cm²/Vs) like Ge and acceptors canbe incorporated to high density (>1×10¹⁹ cm⁻³), thus the base can bemade ultra-thin while maintaining a low base sheet resistance whichincreases current gain and decreases electron transit time. By addingthe ability to grade the base composition from GeSiSn to GeSn such thatthe bandgap energy of the material is gradually reduced throughout thebase as described in these configurations. This grading causes anelectric field, which in turn reduces the transit time, thus increasingF_(t). GeSiSn may be an indirect semiconductor thus reducing radiativerecombination in the base region. GeSiSn for low Sn concentration hasshallow acceptors, so the hole concentration is generally equal to theacceptor doping level and independent of temperature. GeSiSn can beheavily doped P-type.

Exemplary GaN Collector Advantages: GaN collector can be grown on GaN,SiC (many polytypes, i.e., 3C, 4H, 6H), Si, Sapphire, GaAs, and templatesubstrates. Thus the substrate can be chosen to enhance the propertiesof the device. For instance for high power devices it can be useful togrow the GaN on SiC substrates because they have a thermal conductivity.Typically GaN comes in the wurtzite and cubic phase. GaN (wurzite andcubic form) has a large lattice mismatch with GeSn, thus wafer bondingcircumvents the problem of growing strained and incompatible layers. GaNhas high breakdown field, which is excellent for the collector breakdownvoltage. GaN has small conduction band offset with GaAs, thus minimizingthe blocking field at the interface. The use of GaN (instead of GaAs)collector significantly increases the overall thermal conductivity ofthe material structure. GaN has a high saturation velocity, thuselectrons travel without intervalley scattering.

The NPN GaAs—GeSiSn—GaN HBT (referred to as GeSiSn HBT) as compared tostandard NPN InGaP—GaAs—GaAs HBT (referred as GaAs HBT) would have thefollowing advantages. The differences between the two devices mostlyrely on the base material GeSiSn and the collector material GaN.

A commonly used metric for comparing various semiconductors is theJohnson's figure of merit (FOM), which compares different semiconductorsfor suitability for high frequency power transistor applications. Table16 shows a comparison Johnson FOM for Si, GaAs, and GaN.

TABLE 16 Johnson FOM for Si, GaAs, and GaN. Si GaAs GaN Energy Bandgap(eV) E_(gap) 1.1 1.4 3.4 Electron Saturation Velocity (cm/s) V_(sat) 1 ×10⁷   1 × 10⁷ 1.5 × 10⁷ Peak Electron Saturation Velocity 1 × 10⁷ 1.9 ×10⁷ 2.5 × 10⁷ (cm/s) V_(sat peak) Normalized Johnson Figure of Merit 1  9.5 572    (E_(gap) ⁴ × V_(sat peak) ²) Johnson Figure of Merit =Maximum power times frequency ≈ E_(gap) ⁴ × V_(sat) ²

Advantage 2: Because GaN has such large breakdown voltage for examplefor a GeSiSn—GaN base collector junction where the GaN collector is only5000 Å thick, the breakdown voltage is greater than 100 V. A typicalGaAs heterojunction base-collector, where the GaAs collector is over10000 Å thick has a breakdown voltage of only 20 volts. Thus one canreduce the GaN collector thickness as compared to the GaAs, withouthurting robustness, thus the transit time or F_(t) is increased becauseof a thinner base and collector, which in turn increases the F_(max)with another factor because of the low resistivity GeSn base. Typicalvalues of F_(t) and F_(max) should be greater than 150 GHz.

Exemplary Wafer Bonding of GeSiSn Stack to GaN: The method of waferbonding is chosen as the most direct means of forming the GeSn to theGaN structure. A pneumatic bonder can eliminate the problems associatedwith the more conventional torqued jig fixtures. Using the methoddescribed here, the bonder allows gradual pressure application for thedelicate bonding of GeSiSn and GaN. The large size heaters in the platesprovide fast temperature ramp up for the bonding process. The bonder hasa self-leveling action to the surface mechanism and ensures that it isflat with the surface.

The wafer bonders have a unique feature in that the top and bottomplates are under electronically controlled differential air pressure.There is no non-linear return spring force needing to be concerned. Thetop plate moving up and down relies on the differential air pressure inthe top plate's air cylinder; and thus, the bonding pressure can becontinuously adjusted precisely to provide controlled wafer bondingconditions. The wafer bonding system has precise temperature andpressure control to ensure the bonding of the materials. Operation step1 comprises lowering the wafer bonder top plate so that it barelytouches the materials to be bonded. Pressure is then slowly applied atthis time and the temperature of the bonder top and bottom plate areraised. Independent temperature control of the top and bottom platetemperatures allows the accommodation of materials that may havedifferent thermal expansion coefficients, thus minimizing stress to thebonded interface. The bonders can reach temperatures above 500° C. invarious gas ambients, but typically a nitrogen purge is used during thebonding process. The bonders can accommodate up to 4″ diameter wafers.In a single step a PN homojunction or heterojunction bonded materialscan be formed.

FIG. 62 shows a pneumatic wafer bonder configuration 6200. The bonderuses differential air pressure between P1 pressure 6201 and P2 pressure6202, where the pressure is measured by the differential pressure gauge6203. The pressure controls the action of the top plate 6204 in movingdown to clamp the device and substrate 6207, which sits on the bottomplate 6205, which has a ball bearing 6206 for conformal leveling action.Two independent temperature controllers control the temperature of thetop plate 6204 and bottom plate 6205.

Table 17 shows an exemplary wafer bonding process.

TABLE 17 Exemplary Wafer Bonding Process. Step Description 1 The waferis cleaved to appropriate size. 2 Semiconductor materials are thoroughlycleaned. 3 Oxides are removed from surface by chemical etch or plasmaetch. 4 GeSiSn stack material and the GaN material are placed on top ofeach other. 5 GeSiSn and GaN materials are placed in wafer bonder, whichunder low pressure (<5 psi) joins the materials together at possibletemperatures of 24° C. up to 600° C. for 15 min to 60 min. In a gasambient or vacuum. 6 The composite structure is cooled and then removed.7 The composite unit acts as a monolithic PN structure. 8 Currentvoltage testing of the PN junction. 9 Shear test to evaluate thestrength of wafer bonded junction.

Wafer bonding allows formation of a heterointerface without having toperform heteroepitaxy of two poorly matched materials.

FIG. 63 shows the current-voltage characteristic of the wafer bonded PGeSn to N—GaN showing PN rectifying behavior. The vertical axis iscurrent in units of mA, and the horizontal axis is voltage in units ofV. The turn-on voltage of the device may be less than 0.5 V.

The wafer bonding process may allow for independent enhancement ofmaterials without regard to lattice matching. It should be noted that Gelattice constant may be about 5.65 Å and GaN may be about 4.4 Å, whichis a huge mismatch (28%). Interface defects can be minimized by varyingwafer bonding parameters such as oxide removal, temperature, time, andpressure. Table 18 lists the thermal expansion coefficients of the GaAs,GeSn, and GaN. Because the thermal expansion coefficients of all thematerials are similar, the thermal stress generated during wafer bondingshould be minimal.

TABLE 18 Thermal Expansion Coefficients of GaAs, GeSiSn, and GaN.Thermal Expansion Material Coefficient (10⁻⁶ K⁻¹) @ 300 K GaAs 6.0 GeSnsimilar to Ge (low Sn %) 5.9 GaN 5.6

Exemplary Configuration 5B: NPN InGaP Emitter-GeSiSn Base-GaN CollectorDouble HBT with all dissimilar materials Desirable combination ofsemiconductors. To further improve on Configuration 5A, an InGaP emitterregion is added that is lattice matched to GaAs. This device comprisesan emitter stack of InGaP—GeSiSn wafer bonded to a GaN collector. GaNwith it high bandgap offers tremendous improvements in the breakdownvoltage of the HBT. Note the InGaP layer can be compositionally gradedto enhance device performance. The monolithic InGaP—GeSiSn—GaN stack mayhave a conduction band offset though the device less than 0.1 eV. Thisspecial property may allow for the formation of heterojunctiontransistor structure that can have large gain, and large breakdownvoltage (GaN has large breakdown electric field strength and highsaturated velocity). These material characteristics can make a desirablebipolar transistor. The InGaP—GeSiSn—GaN materials stack can bedesirable for making NPN HBTs that can outperform standard SiGe, GaAs,and InP heterojunction bipolar transistors.

FIG. 64 shows the exemplary flat band energy band diagram of NPN InGaPEmitter-GeSiSn Base-GaN Collector Double HBT 6400. This new materialstructure with possibly a near zero conduction band offsets betweeninterfaces and large valence band offsets at the emitter-base and basecollector heterojunction may be a improvement over existing HBTtechnologies. Electrons can easily be injected from the InGaP emitterthrough the GeSiSn base to the GaN collector. Conduction band offsets atemitter-base and base-collector junctions may be small, with largevalence band offsets between the InGaP—GeSiSn and GeSiSn—GaNheterojunctions. The band alignments are desirable for high performanceHBTs. Here an emitter up emitter-base stack 6405 comprising N⁻ emitterordered InGaP 6402 and a P⁺ Base GeSiSn 5803 structure. The orderedInGaP 6402 may have a conduction band offset ΔE_(C)<0.2 eV with theGeSiSn 5803. This emitter-base stack 6405 is then wafer bonded to the N⁻collector GaN 5804 thus forming a wafer bonded junction 6401 at thebase-collector interface. The methodology of wafer bonding thisemitter-base stack is described in Exemplary ELO Wafer BondingConfiguration 6A. Note the conduction band offset ΔE_(C) may be smallthrough the NPN HBT structure.

InGaP semiconductor can be grown epitaxially and may be latticed matchedto GaAs at the composition In_(0.49)Ga_(0.51)P. If typically grown athigh temperatures, it can grow in an ordered phase where the crystallinestructure forms sheets of In—P and Ga—P atoms can alternate in the (001)planes of the FCC unit cell without the intermixing of the Ga and Inatoms on the lattice planes. The ordered InGaP results in a smallconduction band discontinuity between the InGaP and GaAs and is calledthe ordered phase (this can be of weakly type I or weakly type IIbecause it is close to zero). With different growth conditions, the Inand Ga atoms can intermix and the disordered InGaP phase can form, whichhas a conduction band offset (0.1 eV vs. 0.03 eV for the ordered phase)with GaAs.

The base can be graded from GeSiSn to GeSn to have electric fieldenhancement of the charge carriers.

FIG. 65 shows an exemplary flat band energy diagram of the NPNInGaP-graded GeSiSn to GeSn—GaN HBT 6500. Here for variation a base upemitter-base stack 6505 comprising P⁺ Base compositionally gradedGeSiSn—GeSn 6503 grown on a N⁻ emitter disordered InGaP 6502 structure.The compositionally graded GeSiSn—GeSn 6503 layer can comprise at theemitter-base interface a lattice matched or near latticed matched orstrained Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAs, where the GeSiSn may becompositionally graded by reducing the Si content and increasing Gecontent to GeSn at the collector interface. The grading range can gofrom GeSiSn at the emitter-base junction to GeSn at the base-collectorjunction at various compositions. This emitter-base stack 6505 is thenwafer bonded with the P⁺ Base next to the N⁻ collector GaN 5804 thusforming a wafer bonded junction 6501 at the base-collector interface.Due to the compositional grading of the GeSiSn—GeSn 6503 in the P⁺ Base,there is a field enhancement region 6506 that accelerates the carrierstoward the collector. The methodology of wafer bonding the emitter-basestack to the GaN is described in Exemplary Inverted Wafer BondingConfiguration 6B. Note the conduction band offset ΔE_(C) may be smallthrough the NPN HBT structure. Note the differences between flat bandenergy diagrams FIG. 63 with the ordered InGaP and FIG. 64 withdisordered InGaP is small.

Exemplary InGaP (In_(0.49)Ga_(0.51)P) Emitter Advantages: The largevalence band offset between InGaP emitter and GeSiSn base stops backinjection of holes into the emitter. This allows for low N-type dopingof the emitter and high P-type doping of the base, thus lowering baseemitter capacitance while still achieving sizable current gain. Theconduction offset between the InGaP and the GeSn base can be less than0.2 eV, which may be desirable for electron injection into the baselayer. Ordered InGaP may have reduced temperature sensitivity to thecurrent gain. InGaP can be latticed matched to GaAs or Ge or GeSiSn (lowSn %), which enables dislocation free growth.

Table 19 shows an exemplary epitaxial structure of NPN InGaP—GeSiSn—GaNHBT grown and wafer bonded. In this structure the GaN is wurtzitehexagonal structure, “a” or “m” plane material. GaN in this form has nopolarization charge that degrades the base-collector performance.Non-polar GaN wurzite substrates are illustrated here though one coulduse SiC, GaAs, Si, sapphire (non-polar and polar forms). GaN (FCC) canalso be grown on GaAs which also lacks polarization charge effects.

TABLE 19 Epitaxial Structure of NPN InGaP—GeSiSn—GaN HBT. Layer LayerName Description Comment 1 N⁺ Cap ~1000 Å InGaAs (Te-doped >10¹⁹ cm⁻³) 2N− Emitter Cap ~1500 Å GaAs (Si-doped ~5 × 10¹⁸ cm⁻³) 3 N− Emitter ~500Å InGaP (Si-doped ~3 × 10¹⁷ cm⁻³) Ordered or disordered 4 P⁺ Base ~500 ÅGe_(1−z)(Si_(0.8)Sn_(0.2))_(z) Latticed matched can be B-doped >10¹⁹cm⁻³) or 0 < Si % ≤ 40% Can be 0 ≤ Sn % ≤ 10% compositionally Thicknessrange 100 Å-5000 Å graded GeSiSn—GeSn 5 N− Collector ~10000 Å Non-polarGaN (Si-doped ~1 × 10¹⁸ cm⁻³) Wafer bonded to above 6 N⁺ Sub-Collector~5000 Å Non-polar GaN (Si-doped ~5 × 10¹⁸ cm⁻³) 7 Substrate Non-polarGaN N⁺ conducting substrate Crystalline Note the compositionally gradedGeSiSn—GeSn layer can comprise at the emitter-base interface a latticematched or near latticed matched or strainedGe_(1−z)(Si_(0.8)Sn_(0.2))_(z) to GaAs, where the GeSiSn may becompositionally graded by reducing the Si content and increasing Gecontent to GeSn at the collector interface. The grading range can gofrom GeSiSn at the emitter-base junction to GeSn at the base-collectorjunction various compositions. Note the dopants listed are only one ofmany possible dopants, and does preclude the use of other dopants anddoping values are only nominal values but can take on many variations.The thicknesses are all exemplary and can take on many different values.

Exemplary Advantages of InGaP—GeSiSn—GaN HBT Technology: The NPNInGaP—GeSiSn—GaN stack minimizes the conduction band offsets, whichhinder electron transport (ultra-fast transistor action). The followingsemiconductor materials may enhance transistor performance: GaNcollector, GeSiSn base, InGaP emitter. Wafer bonding allows for theintegration of GaN without having to perform lattice-mismatch growth.Wafer bonding is desirable for GaN—GeSiSn because the thermal expansioncoefficients are close to each other. Strain effects can be incorporatedin this device because the alloy composition of the InGaP can be changedto introduce tensile or compressive strain.

GaN collector for its high saturation velocity and large bandgap energywhich results in a high breakdown voltage. In examples described herein,the GaN can be grown on the various substrates like sapphire or variousSiC polymorphs or Si or GaAs or GaN or diamond or template substrates.Polar GaN wurtzite structure can be grown on sapphire or SiC (manypolytypes: 3C, 4H, 6H, etc.) or Si substrates, or GaN substrates ortemplate substrates and may have piezoelectric and polarization charge.GaN is grown in the wurtzite (hexagonal) phase results in largespontaneous and piezoelectric polarization charge thus possibly creatinga potential energy barrier at the wafer-bonded GeSiSn—GaN base/collectorinterface. Non-polar GaN cubic (FCC) structure can be grown on GaAs orSi or GaN or template substrates. GaN in this form has no polarizationcharge that degrades the base-collector performance. A cubic form of GaNwith (001) orientation can be grown on zinc-blende GaAs. Thus the cubicGaN can be grown on conducting GaAs which can act as the sub-collector.The zinc-blende (cubic) GaN collector has a negligible conduction bandoffset with respect to the GeSiSn base. The conduction band offsetbetween GaAs and cubic GaN may be roughly ΔE_(C)<0.1 eV. Thus the GeSiSn(close to Ge) conduction band offset to GaN may be about ΔE_(C)<0.1 eVat the base/collector heterojunction. Non-polar wurtzite forms, are cutfrom the c-plane growth along the “a” or “m” plane directions. If theGaN is grown along the “m” or “a” plane axis, these polarization effectscan be eliminated. Typical GaN wurzite crystals grown along thedirection (c-plane) of III-nitrides suffer from polarization inducedelectric fields. Electric fields do not exist across nonpolar directions(a-plane or m-plane). Thus, high quality non-polar GaN substratecrystals are produced by slicing a c-plane GaN boule along the “a” or“m” plane. Such a material results in low defect density non-polarsubstrates, which have improved substrates for fabrication of devices.Because Configuration 5A showed the wafer bonding of emitter stack to apolar GaN collector, for this Configuration 5B a non-polar GaN substrateis demonstrated.

The (ordered or disordered) InGaP—GeSiSn emitter base junction has alarge valence offset which may be greater than 1.0 eV and a smallconduction band offset. This eliminates the back injection of holes tothe emitter from the base, which reduces the gain of the transistor.Also because this is a double HBT, the offset voltage in the outputcharacteristic is reduced thus enhancing the power added efficiency. Thebase is doped heavily P⁺ (typically >1×10¹⁹ cm⁻³), with such high dopingof the base, the emitter valence band offset blocks the holes eventhough the base doping is much higher than the N⁻ emitter doping (low10¹⁷ cm⁻³).

In some examples, a feature described herein can be the formation of anadvanced manufacturing platform to demonstrate a possibly noveltransistor semiconductor stack, which cannot be grown with standardcrystal growth methodologies. The uniqueness of the device describedherein may lie in the small conduction band offset (less than <0.1 eV)through the three different semiconductor materials (InGaP—GeSiSn—GaN)emitter-base-collector may enhance overall HBT performance, which isimpossible to grow by standard crystal growth techniques. The parametersthat InGaP—GeSiSn—GaN NPN transistor can achieve are the following:double heterojunction, emitter-base, and base collector can reduceoffset voltage; high gain (large valence band offset at emitter basejunction); high breakdown voltages for improved ruggedness for highpower applications; and a short collector structure can result inimproved electron transit time.

Exemplary ELO Wafer Bonding Configuration 6A: Fabrication of InGaPEmitter-GeSiSn Base-GaN Collector double HBT as an example of the ELOwafer bonding device fabrication process. For Configuration 6A anepitaxial lift off (ELO) process and wafer bonding can be used tofabricate the emitter/base stack to the GaN collector. Epitaxial liftoff and wafer bonding process is a quick-turn method for integration offabricated GeSiSn devices to be joined on the GaN substrate. Combiningthe techniques of epitaxial lift off and wafer bonding releases therestrictions of lattice matching imposed by epitaxial growth and opensnew degrees of freedom for the design of semiconductor devices, becausethe combination of unique properties of different materials becomespossible.

FIG. 66 shows a schematic methodology of the epitaxial lift off process6600. An epitaxial layer stack top HBT 6608 (pre-processed top half ofthe HBT device: InGaP emitter/GeSiSn base stack) is grown on asacrificial GaAs 6606 substrate with a thin aluminum arsenide (AlAs6607) etch layer inserted in between the two layers. The top HBT 6608 iscovered with wax 6609 for mechanical strength. This thin AlAs separationlayer 6607 is removed by etching in hydrofluoric acid (HF etch AlAs6610) in order to lift off the epitaxial layers from the GaAs 6606substrate. The wax 6609 protecting the top HBT 6608 without the GaAs6606 substrate is then transferred onto a new substrate like GaN 6611via Van der Waals forces. This technique allow for the clean and flatsurfaces of two dissimilar materials to be brought into close proximitywhere attractive forces pull them together, forming an intimate contactbetween different materials. The strength of the adhesion depends on thetype of interaction. Van der Waals forces provide the first step ofattraction. The bonding strength can be increased in the materials bywafer bonding at elevated temperatures. FIG. 66 which demonstrates anexemplary epitaxial lift off (ELO) process 6600 can be described asfollows: (6601) epitaxial HBT stack layer growth with AlAs separationlayer 6607, top HBT 6608 on GaAs 6606 with AlAs 6607; (6602) Wax 6609covers top HBT 6608, epitaxial lift off by HF etch AlAs 6610 removesAlAs 6607 and releases the top layer off of GaAs 6606 substrate; (6603)Van der Waals bonding by surface tension of the top HBT 6608 to GaN 6611substrate; (6604) removal of wax from top HBT 6608 on GaN 6611; and(6605) then wafer bonding to further strengthen the top HBT/GaNmonolithic structure.

Exemplary details of device fabrication and growth of ELO top half(example: InGaP—GeSiSn—GaN HBT).

FIG. 67 shows the schematic of the top half of the HBT InGaPemitter/GeSn base stack 6701 with the inclusion of the AlAs separationlayer 6703. Note the separation layer could be AlGaAs from 40% to 100%Al. The top half of the HBT InGaP emitter/GeSn base stack 6701comprises: a sacrificial GaAs substrate 6702; AlAs separation layer6703; P⁺ GeSiSn Base 6704; N⁻ InGaP emitter 6705; N⁺ GaAs contact 6706epitaxial stack. This top half of the HBT InGaP emitter/GeSn base stack6701 is then wafer bonded to the GaN collector stack 6707. The GaNcollector stack 6707 comprises a starting N⁺ SiC 4H substrate 6708, withan N⁺ SiC sub-collector 6709, then finally an N⁻ GaN collector 6710.There could be many different variations of the GaN collector stack6707, such as growth on GaN, Si, GaAs, sapphire substrates, or templatesubstrates.

Table 20 shows an exemplary structure top half of the HBT InGaPemitter/GeSiSn base stack 6701.

TABLE 20 Exemplary structure top half of the HBT InGaP emitter/GeSn basestack 6701. Layer Layer Name Description Comment 1 N⁺ Cap (non-alloyed)~1,000 Å InGaAs (Te-doped >10¹⁹ cm⁻³) 2 N− Emitter Cap ~1500 Å GaAs(Si-doped ~5 × 10¹⁸ cm⁻³) 3 N− Emitter ~500 Å In_(0.49)Ga_(0.51)P(Si-doped ~3 × 10¹⁷ cm⁻³) Ordered or disordered 4 P⁺ Base ~500 ÅGe_(1−z)(Si_(0.8)Sn_(0.2))_(z) Latticed matched can be B-doped >10¹⁹cm⁻³ or 0 < Si % ≤ 40% Can be 0 ≤ Sn % ≤ 10% compositionally Thicknessrange 100 Å-5000 Å graded GeSiSn—GeSn 5 Separation ~50 Å AlAs Layerremoved 6 High Purity Buffer ~500 Å GaAs (un-doped) 7 Sacrificial GaAsSemi-insulating or conducting Substrate Note the dopants listed are onlyone of many possible dopants, and does preclude the use of other dopantsand doping values are only nominal values but can take on manyvariations. The thicknesses are all exemplary and can take on manydifferent values.

Table 21 shows an exemplary GaN collector structure 6707. Note that theGaN collector can be grown on Si, SiC, GaAs, Sapphire, GaN, etc.,substrates.

Table 22 shows an exemplary GaN collector structure 6707 with a seedadhesion layer which can be GeSiSn, AlN, AlGaN, InGaN or InAlN. Anexemplary SiC collector structure could also be used as shown by theTable 23.

TABLE 21 Exemplary GaN Collector Structure 6707. Layer Layer NameDescription Comment 1 N⁻ Collector ~10,000 Å GaN (Si-doped ~1 × 10¹⁶cm⁻³) Wurtzite phase 2 N⁺ Sub-Collector ~5,000 Å 4H SiC (N-doped ~5 ×10¹⁸ cm⁻³) Standard (nitrogen doped) 3 N⁺ Buffer ~500 Å 4H SiC 4 4H SiC(conducting substrate) N⁺ substrate: other phases of SiC possible

TABLE 22 Exemplary GaN Collector Structure 6707 with adhesion layersLayer Layer Name Description Comment 1 Seed adhesion ~50 Å GeSiSn(undoped or p-doped or n- Thickness range layer or electrical doped10-5000 Å performance Or InAlN enhancement layer Or AlN Or AlGaN OrInGaN Or InN 2 N⁻ Collector ~10,000 Å GaN (Si-doped ~1 × 10¹⁶ cm⁻³)Wurtzite phase 3 N⁺ Sub-Collector ~5,000 Å 4H SiC (N-doped ~5 × 10¹⁸cm⁻³) Standard (nitrogen doped) 4 N⁺ Buffer ~500 Å 4H SiC 4 4H SiC(conducting substrate) N⁺ substrate: other phases of SiC possible

TABLE 23 Exemplary SiC Collector Structure. Layer Layer Name DescriptionComment 1 Seed adhesion ~50 Å GeSiSn (undoped or p-doped or Thicknessrange layer or electrical n-doped) 10-5000 Å performance Or InAlNenhancement layer Or AlN Or AlGaN Or InGaN Or InN. 2 N⁻ Collector~10,000 Å SiC (N-doped ~1 × 10¹⁶ cm⁻³) nitrogen-doped 3 N⁺ Sub-Collector~5,000 Å 4H or 6H SiC (N-doped Standard (nitrogen ~5 × 10¹⁸ cm⁻³) doped)4 N⁺ Buffer ~500 Å 4H or 6H SiC 5 4H or 6H SiC (conducting substrate) N⁺substrate: other phases of SiC possible.

From this point the device to wafer bonded can be pre-processed orpost-processed. For this first exemplary configuration the ELO devicedemonstrated is pre-processed (device has been partially fabricated).The pre-processed top half of HBT is covered in a “black wax” (ApiezonW) or “white wax” (crystal bond) or other type of adhesive. In someexamples, it is useful to place a mechanical holder like an exemplarysapphire mechanical substrate to the wax for rigidity and a mechanicalstrength. The separation AIAs layer is undercut in hydrofluoric HF acidand deionized water at room temperature at various ratios. After releasethe etchant is diluted with de-ionized water, the wax-covered ELOstructure is moved to the GaN substrate where Van der Waals bondingoccurs. In various embodiments, the adhesion process is handled in waterto minimize contamination of the surfaces.

FIG. 68 shows a pre-processed top half of the HBT which comprises the N⁺GaAs contact 6706; N⁻ InGaP emitter 6705; P⁺ GeSiSn base 6704; AlAsseparation layer 6703 on GaAs substrate 6702; mesa device structure withemitter contact 6801; and base contact 6802. Next comes the HF etch ofAlAs and ELO 6807 step. Before etching the device, an adhesive like wax6808 is melted on pre-processed fabricated Top Half of HBT 6800 andsometimes it can be useful to have a mechanical substrate 6810 place onthe wax for mechanical strength. This can be useful in large waferdevices (2″, 3″, 4″, 6″, 12″, 18″, etc., wafer sizes and not onlylimited to these sizes). For the ELO process the wax 6808 coatedpre-processed fabricated Top Half of HBT 6800 assembly is placed into asolution of anhydrous hydrofluoric (HF) acid and over time the waxcoated top half of the HBT 6809 is removed from the sacrificial GaAssubstrate 6702. The solution can be heated and temperature controlled,the lift off process time depends on area of the device, and can takefrom several minutes to many hours. Once the sample is lift off, the waxprovides for mechanical strength of the lifted off layer and allows forease of transport to the GaN substrate.

FIG. 69 shows where the top half of HBT wafer bonded to collectorstructure 6901, which comprises the wax coated top of the HBT 6809placed on the GaN collector structure 6707 with van der Waals bonding.Note the GaN collector could have a layer to electrically enhanceperformance, which can be deposited by PLD any other epitaxial process.There are many other seed layers that could be used for this purpose.The seed layer could be used for adhesion or modifying the electricalinterface properties of the heterojunction to improve performance orreliability. Some seed layers that may be used are GeSiSn, AlN, AlGaN,InAlN, InGaN, InN.

Initially, the wax coated top of the HBT 6809 placed on the GaNcollector structure 6707 with van der Waals bonding results in theadhesion of these layers. The structure can be put intotrichloroethylene or acetone or some solvent to remove the wax, whichthen forms the wafer bonded HBT 6902. To finalize the device for test, abottom metal contact 6903 is applied to the N⁺ SiC 4H substrate 6708.The final wafer bonded structure can then be placed in a wafer bonder,and under heat and pressure, stronger bond formation between the tophalf of the HBT and the GaN collector structure 6707 should result for apermanent final structure. Finally, bottom metallization of thestructure allows for the testing of this heterojunction bipolarstructure for DC testing in a standard emitter-base-collectorconfiguration.

Exemplary Inverted Wafer Bonding Configuration 6B: Device Fabrication &Growth of inverted top half of the GeSiSn base HBT for wafer bonding andpost-processing. It can be useful to use an inverted top of the HBT forwafer bonding.

FIG. 70 shows an inverted top half of HBT 7000. This comprises growth ona sacrificial GaAs substrate 7001; followed by a latticed matched InGaPetch stop 7002; then an N⁺ contact GaAs 7003; then an N⁻ GaAs emitter7004; and then the P⁺ GeSiSn base 7005. Table 24 shows an exemplarydesign of the structure.

TABLE 24 Exemplary epitaxial structure of the inverted top half of HBT.Layer Layer Name Description Comment 1 P⁺ Base ~500 ÅGe_(1−z)(Si_(0.8)Sn_(0.2))_(z) Latticed matched can be B-doped >10¹⁹cm⁻³ or 0 < Si % ≤ 40% Can be compositionally 0 ≤ Sn % ≤ 10% gradedGeSiSn—GeSn Thickness range 100 Å-5000 Å 2 N⁻ Emitter ~500 ÅIn_(0.49)Ga_(0.51)P (Si-doped ~3 × 10¹⁷ cm⁻³) Ordered or disordered 3 N⁻Emitter Cap ~1500 Å GaAs (Si-doped ~5 × 10¹⁸ cm⁻³) 4 N⁺ Contact ~1000 ÅGaAs (Si-doped ~5 × 10¹⁸ cm⁻³) 5 ~50 Å InGaP Stop Etch 6 High PurityBuffer ~500 Å GaAs UID 7 Sacrificial GaAs substrate Semi-insulating orconducting

FIG. 71 shows the straightforward wafer bonding 7101 of the inverted tophalf of HBT 7000 to the GaN collector structure 6707. This step showsthe final wafer bonded structure 7102 and removal of the sacrificialGaAs substrate and InGaP stop etch. The wafer bonded junction occurs atthe P⁺ GeSiSn base to the N− GaN collector. The wafer bonding processwould occur under heat, pressure, time, current/voltage bias, gaseousenvironment, etc. The final step is the wafer bonded structure andremoval of sacrificial GaAs substrate 7001 and InGaP Stop etch 7002.Thus, after wafer bonding, the sacrificial GaAs substrate 7001 and InGaPetch stop 7002 would be removed by lapping (thinning) and then etchingto the InGaP etch stop layer. This leaves the final epitaxial waferbonded HBT structure 7103.

FIG. 72 shows the post-processing of final epitaxial wafer bonded HBTstructure 7103, where a standard quick lot HBT device fabricationprocedure can be used to test the HBT. The device fabrication of thestructure relies on standard GaAs fabrication techniques because thewafer bonded junction 7204 never gets exposed to any of the chemicalprocesses. This standard device processing technology is used for thefabrication of HBTs and can be generally used for all the differentconfigurations previously elucidated. This HBT test mask set providesimmediate feedback for fine tuning the growth process HBT devicefabricated using a Quick lot mask set. There are many methodologies forthe fabrication of the HBT. One possible version is to apply photoresistacross the surface of the HBT structure 7103. A photomask is placed onthe photoresist surface and exposed with UV light which imprints apattern of the emitter metal contact 7201 across the surface. Next, theHBT structure 7103 with exposed photoresist is put into a developersolution. The pattern is developed and then metal is blanket coatedacross the surface using a metal evaporator. The whole structure is putinto acetone which dissolves the photoresist leaving only emitter metalcontact 7201 pattern across the top of the N⁺ GaAs contact 7003.

The emitter metal contact 7201 then can act as a metal mask for mesaetching the HBT structure 7103 down to the P⁺ GeSiSn Base 7005. Here,photoresist is spun all over the mesa etched structure. With a photomaskthat has base metal contact 7202 pattern is placed on the photoresist.The photomask covering the photoresist is subsequently exposed with UVlight and then developed to open a pattern where the base metal contact7202 can be deposited on the P⁺ GeSiSn base 7005. Typically a metalevaporator deposits blanket metal all over the surface of the mesaetched structure. The structure is then put in acetone for metal liftoff, thus resulting in a pattern of base metal contact 7202 on the P⁺GeSiSn Base 7005.

Next, back metallization or the bottom metal contact 7203 is applied tothe N⁺ SiC 4H substrate 6708. FIG. 72 shows the final wafer bonded HBTstructure 7200. Sometimes the HBT device needs to be alloyed at elevatedtemperature to activate the metal contacts. The device is ready for DCtesting.

Typical parameters that are measured and used to qualify the HBTmaterials are sheet resistance of the emitter, base and sub-collector byboth TLM and van Der Pauw cross structures. Various sized HBTs (emittersizes are 40×40, 50×50, 75×75, 100×100 μm²) are used to determineeffects of geometry to device parameters such as Gummel, Gain, OutputCharacteristics and breakdown voltages.

Exemplary Configuration 7: NPN GaAs Emitter-GeSiSn Base-GaN (or SiC)Collector Double heterojunction with all dissimilar materials which mayhave a small Conduction Band Offset between Emitter-Base-Collector.GaAs—GeSiSn—GaN heterojunction bipolar transistor (HBT), as describedherein, embodies RF power output, ruggedness, high bandwidth and goodlinearity, and when combined with low turn-on voltage is desirable forminimizing power consumption. The arrangement of materials describedherein combines high transconductance, enormous breakdown voltage (GaNcollector), and a desirable emitter-base heterojunction (wide bandgapGaAs emitter on a narrow bandgap GeSiSn high conductivity p-type base).The huge breakdown field of GaN may allow the use of short collectordevices with high bandwidths (cut-off frequency f_(T) and maximumoscillation frequency f_(max)).

A combination of semiconductors for transistors by utilizing a favorableconduction band alignment between the emitter-base-collector junctions,thus forming a possibly enhanced heterojunction bipolar transistor: Asmall conduction band offset may exist between GaAs (emitter)-GeSiSn(base)-GaN (collector). The P-type GeSiSn base may be lattice matched toN-type GaAs emitter (GeSiSn/GaAs stack). GaN collector can be grown ondifferent N⁺ substrates. Monolithic integration of materials by waferbonding of GeSiSn/GaAs stack wafer to the N-type GaN collector(circumvents large lattice mismatched growth).

The monolithic GaAs—GeSiSn—GaN stack may have a small conduction bandoffset through the device. This property allows for the formation ofheterojunction transistor structure that can have large gain (largevalence band offset between GaAs emitter and GeSiSn base). Thesematerials allow for a low base sheet resistance, low turn-on voltage,and large breakdown voltage (GaN has large breakdown electric fieldstrength and high saturated velocity). These material characteristicsmake for a desirable bipolar transistor. The GaAs—GeSiSn—GaN materialsstack may be desirable for making NPN HBTs that can significantlyoutperform standard high power GaN transistors.

FIG. 73 shows an exemplary flat band energy diagram of the NPN GaAsEmitter-GeSiSn Base-GaN 7300 (or SiC) Collector Double heterojunctionwith all dissimilar materials having a small conduction band offsetbetween the Emitter-Base-Collector. Here an emitter up emitter-basestack 7306 comprising of N⁻ emitter GaAs 7301 and P⁺ base GeSiSn 7302structure. The full monolithic structure can be formed using anepitaxial lift off (ELO) procedure. This emitter-base stack 7306 iswafer bonded to collector stack 7307 thus forming a wafer bondedjunction 7310 at the base-collector interface. The wurtzite N⁻ collectorGaN 7303 can be grown on 4H or 6H (or other variations) N⁺ sub-collectorSiC 7304, and comprise the collector stack 7307. Possible methodologiesof wafer bonding this emitter-base stack 7306 to the collector stack7307 is described in Exemplary ELO Wafer Bonding Configuration 6A and inExemplary Inverted Wafer Bonding Configuration 6B. Note the conductionband offset ΔE_(C) may be small through the NPN HBT structure. The banddiagram of this new material structure with small conduction bandoffsets between interfaces and a large valence band offset at theemitter-base heterojunction allows for electrons to be easily injectedfrom the GaAs emitter through the Ge base to the GaN collector. Note aGeSn base can be used in this configuration.

To form such a structure, the interface between the base-emitter stack7306 and the collector stack 7307 can require wafer bonding, because thelattice constants of the base material and collector material are highlylattice mismatched.

An exemplary structure that could be grown and wafer bonded isillustrated in the following table. Table 25 shows an exemplaryepitaxial structure of an NPN GaAs—GeSiSn-Hexagonal GaN wafer bondedHBT. In this structure, the GaN is grown on SiC which is a typicalsubstrate for the growth and one of the many described substrates thatcan be used. SiC is preferred for high power electronics because it hasthe highest thermal conductivity between GaN, Si, GaAs and sapphire theother primary substrates for GaN. In this structure, GaN can be grown onwurtzite GaN or 4H SiC, or other SiC polymorphs or GaN or Si or Sapphireor Diamond or GaAs substrates.

TABLE 25 Epitaxial Structure of NPN GaAs—Ge-Hexagonal GaN HBT. LayerLayer Name Description Comment 1 N⁺ Cap (non-alloyed) ~1000 Å InGaAs(Te-doped >10¹⁹ cm⁻³) Standard 2 N⁻ Emitter Cap ~1500 Å GaAs (Si-doped~5 × 10¹⁸ cm⁻³) Standard 3 N⁻ Emitter ~500 Å GaAs (Si-doped ~3 × 10¹⁷cm⁻³) Standard (InGaP can also be used as the emitter) 4 P⁺ Base ~500 ÅGe_(1−z)(Si_(0.8)Sn_(0.2))_(z) Latticed matched can be B-doped >10¹⁹cm⁻³ or 0 < Si % ≤ 40% Can be compositionally 0 ≤ Sn % ≤ 10% gradedGeSiSn—GeSn Thickness range 100 Å-5000 Å 5 N⁻ Collector ~10000 Å GaN(Si-doped ~1 × 10¹⁶ cm⁻³) Wafer bonded to above 6 N⁺ Sub-Collector ~5000Å 4H SiC (N-doped ~5 × 10¹⁸ cm⁻³) Standard (nitrogen doped) 7 N⁺ Buffer~500 Å 4H SiC Standard 8 4H or 6H SiC (conducting substrate) N⁺Substrate: Excellent thermal conductivity Note the dopants listed areonly one of many possible dopants, and does preclude the use of otherdopants and doping values are only nominal values but can take on manyvariations. The thicknesses are all exemplary and can take on manydifferent values.

In other examples, there is a cubic form of GaN that can be used in theHBT device structure. The GaN can be grown face centered cubic (FCC) on3C SiC. GaN in this form can have no polarization charge that degradesthe base-collector performance. GaN (FCC) can also be grown on Sisubstrates or on template substrates that are commercially available.Ge_(0.98)Si_(0.02) can be latticed matched to GaAs and may have abandgap energy of approximately 0.7 eV (ranging from 0.67 eV to 0.72eV).

FIG. 74 shows an exemplary flat band energy diagram of the NPN GaAsEmitter-GeSi Base-GaN Collector 7400 (or SiC Collector) Doubleheterojunction with all dissimilar materials having a small conductionband offset between Emitter-Base-Collector. Here an emitter upemitter-base stack 7306 comprising of N⁻ emitter GaAs 7301 grown on P⁺base GeSi 7302 structure. The full monolithic structure can be formedusing an epitaxial lift off (ELO) procedure. This emitter-base stack7306 is wafer bonded to collector stack 7407 thus forming a wafer bondedjunction 7410 at the base-collector interface. The cubic N⁻ collectorGaN 7403 can be grown on 3C (or other variations) N⁺ sub-collector SiC7404 (or an N⁺ sub-collector Si 7405), and can comprise the collectorstack 7407. Possible methodologies of wafer bonding this emitter-basestack 7306 to the collector stack 7407 is described in Exemplary ELOWafer Bonding Configuration 6A and in Exemplary Inverted Wafer BondingConfiguration 6B. Note the conduction band offset ΔE_(C) may be lessthan 0.1 eV through the NPN HBT structure. The band diagram of this newmaterial structure may have a small conduction band offsets betweeninterfaces and a large valence band offset at the emitter-baseheterojunction allows for electrons to be easily injected from the GaAsemitter through the GeSi base to the GaN collector.

To form such a structure the interface between the base-emitter stack7306 and the collector stack 7407 can require wafer bonding, because thelattice constants of the base material and collector material are highlylattice mismatched.

GaN in the cubic form has no polarization charge that degrades thebase-collector performance. GaN (FCC) can also be grown on Si substratesor on template substrates that are commercially available. Table 26shows an exemplary epitaxial structure of an NPN GaAs—GeSiSn-Cubic GaNwafer bonded HBT. In this structure, the GaN is grown on SiC which is atypical substrate for the growth and one of the many describedsubstrates that can be used. SiC is preferred for high power electronicsbecause it has the highest thermal conductivity between GaN, Si, GaAsand sapphire the other primary substrates for GaN. In this structure,GaN can be grown on cubic GaN or 3C SiC or Si or other SiC polymorphs orSapphire or Diamond or GaAs.

TABLE 26 Epitaxial Structure of NPN GaAs—GeSiSn-Cubic GaN HBT. LayerLayer Name Description Comment 1 N⁺ Cap (non-alloyed) ~1000 Å InGaAs(Te-doped >10¹⁹ cm⁻³) Standard 2 N⁻ Emitter Cap ~1500 Å GaAs (Si-doped =5 × 10¹⁸ cm⁻³) Standard 3 N⁻ Emitter ~500 Å GaAs (Si-doped = 3 × 10¹⁷cm⁻³) Standard (InGaP can also be used as the emitter) 4 P⁺ Base ~500 ÅGe_(1−z)(Si_(0.8)Sn_(0.2))_(z) Latticed matched can be B-doped >10¹⁹cm⁻³ or 0 < Si % ≤ 40% Can be compositionally 0 ≤ Sn % ≤ 10% gradedGeSiSn—GeSn Thickness range 100 Å-5000 Å 5 N⁻ Collector ~10000 Å GaN(Si-doped ~1 × 10¹⁶ cm⁻³) Wafer bonded to above 6 N⁺ Sub-Collector ~5000Å 3C SiC (N-doped ~5 × 10¹⁸ cm⁻³) Standard (nitrogen doped) 7 N⁺ Buffer~500 Å 3C SiC Standard 8 3C SiC (conducting substrate) N⁺ Substrate:Excellent thermal conductivity Note the dopants listed are only one ofmany possible dopants, and does preclude the use of other dopants anddoping values are only nominal values but can take on many variations.The thicknesses are all exemplary and can take on many different values.The substrate may be other SiC polymorphs or other substrates such asGaN or Si or Sapphire or Diamond or GaAs.

In various embodiments, a thin GeSiSn or InAlN, or AlN or AlGaN, or InN,or InGaN layer can be put on the GaN to promote adhesion of the waferbonding of the GeSiSn to the GaN. This thin film can be grownepitaxially by Metalorganic chemical vapor deposition (MOCVD), molecularbeam epitaxy (MBE), pulsed laser deposition (PLD), or other forms ofdeposition.

The device described herein, a GaAs (emitter)/GeSiSn (base) wafer bondedto four different varieties of GaN collector structures (GaN/GaN,GaN/SiC, GaN/Sapphire, GaN/Si), may result in a possibly a bettercollector structure. GeSiSn can be an desirable base layer due to itslow bandgap energy and the fact it has the highest hole mobility of anysemiconductor.

GaAs Emitter Advantages (InGaP can also be used as the emitter withsimilar advantages): The large valence band offset between GaAs emitterand GeSiSn base stops back injection of holes into the emitter. Thisallows for low n-type doping of the emitter and high p-type doping ofthe base, thus lowering base emitter capacitance while still achievingsizable current gain. GeSiSn can be latticed matched to GaAs whichenables dislocation free growth. The use of AlGaAs or disordered orordered InGaP emitter could also be used in this device structure.

GeSiSn Base Advantages: GeSiSn can have a low bandgap which results inlow turn-on voltage. GeSiSn can have a high hole mobility and acceptorscan be incorporated to high density, thus the base can be madeultra-thin while maintaining a low base sheet resistance which increasescurrent gain and decreases electron transit time. GeSiSn may haveshallow acceptors, so the hole concentration is generally equal to theacceptor doping level and independent of temperature. The low base sheetresistance results in a high f_(max). The surface recombination velocitymay be low for p-type GeSiSn.

GaN Collector Advantages: GaN has a large lattice mismatch with Ge, thuswafer bonding circumvents the problem of growing strained andincompatible layers. GaN collector can be grown on: (1) lattice matchedGaN, (2) 4H SiC, 6H SiC, (3) sapphire, (4) 3C SiC (cubic GaN eliminatesthe polarization charge that arises in Wurzite GaN), (5) on Si, or (6)other substrates. GaN has high breakdown field which is excellent forthe collector breakdown voltage. SiC has many polytypes and only a fewhave been listed above. GaN has a small conduction band offset with Ge,thus small blocking field at the interface. GaAs—Ge—GaN materialstructure avoids the use of ternary alloy semiconductors therebyeliminating alloy scattering of electrons. The GeSiSn base at low Si andSn percents may have all the advantages of the Ge base. GaN collectorsignificantly increases the overall thermal conductivity of the materialstructure. GaN has a high saturation velocity thus electrons travelwithout intervalley scattering. GaN power maximum capability may have572 times greater than that of Si and may have 60 times greater thanthat of GaAs.

FIG. 75 shows bandgap energies of various semiconductors as a functionof the lattice constant. It can be readily seen that new types ofsemiconductor devices could be formed if the lattice matchingconstraints were eliminated. It would then be possible to fabricateheterojunctions based on the materials characteristics instead of thoseconstrained to near lattice constant materials. It is with this aim thatmanufacturing wafer bond methodologies can be used to join dissimilarmaterials to form possibly enhanced state-of-the-art devices.

Ge_(0.98)Si_(0.02) can be latticed matched to GaAs and may have abandgap energy of 0.7 eV (ranging from 0.67 eV to 0.72 eV). GeSi basecan significantly decrease transistor turn-on voltage and therebyincrease the power added efficiency of the device. The GaAs—GeSi—GaNstructure described herein can have the a low turn-on voltage.

FIG. 76 shows a graph of the collector current density J_(C) vs. theturn-on voltages V_(BE) of various HBT material systems. The figureshows a plot of the collector current density J_(C) (A/cm²) verticalscale versus base-emitter voltage V_(BE) (V) horizontal scale. Theplotted characteristics for several different heterojunction bipolartransistor (HBT) technologies are shown. The GeSi HBT structuredescribed herein may have a low turn-on voltage 7601 of the technologiesshown of InP/InGaAs, SiGe, GaAs, and GaN/InGaN.

Summary of Features of GaAs—GeSiSn—GaN HBT materials. The semiconductormaterials stack may form a favorable bipolar transistor: GaAs emitter,GeSiSn base, and GaN collector. The GaAs—GeSiSn—GaN stack may minimizethe conduction band offsets which hinder electron transport (ultra fasttransistor action). GaAs and GeSiSn can be latticed matched and waferbonding allows for the integration of GaN without having to performlattice-mismatch growth. Wafer bonding is desirable for GaAs—GeSiSn—GaNbecause the thermal expansion coefficients are close to each other. GaNcan be grown on GaN, 4H SiC, 6H SiC, 3C SiC, sapphire, or Si substrates,these include the wurtzite and cubic forms.

The GaAs—GeSiSn—GaN NPN heterojunction materials may achieve thefollowing metrics for transistors: (1) Low turn-on voltage; (2) highgain, both large valence band offset and GeSiSn low p-type resistivity;(3) the thin base may enhance the transit time of the electrons acrossthe base (large f_(T)) and high frequency of operation f_(max) (lowerbase sheet resistance=higher f_(max)); and (4) high breakdown voltagesimproves ruggedness and enables higher power applications.

The GaAs—GeSi—GaN NPN heterojunction materials may achieve the followingmetrics for next-generation electronic transistors: (1) Low turn-onvoltage; (2) high gain, both large valence band offset and GeSi lowp-type resistivity, allows the use of a thinner base region; (3) thethin base also enhances the transit time of the electrons across thebase (large f_(T)) and high frequency of operation f_(max) (lower basesheet resistance=higher f_(max)); and (4) high breakdown voltagesimproves ruggedness and enables higher power applications.

Different GaN collector structures include the following: (1) N⁻ GaN(1×10¹⁷ cm⁻³) on N⁺ GaN (>(1×10¹⁹ cm⁻³) substrate, there is zero latticemismatch in this structure; (2) N⁻ GaN (1×10¹⁷ cm⁻³) on N⁺ 4H SiC(>(1×10¹⁹ cm⁻³) substrate, there is about a 4% lattice mismatch betweenthe layers. Presently, SiC is used as the substrate for GaN epitaxy, 6HSiC or various other polytypes may also work; (3) N⁻ GaN (1×10¹⁷ cm⁻³)on N⁺ GaN (>(1×10¹⁹ cm⁻³) grown on sapphire substrates. There may beabout a 14% lattice mismatch between the two layers; (4) N⁻ GaN (1×10¹⁷cm⁻³) on N⁺ 3C SiC (>(1×10¹⁹ cm⁻³) substrate, there is about a 4%lattice mismatch between the layers; (5) Cubic N⁻ GaN (1×10¹⁷ cm⁻³) onN⁺ Si (>(1×10¹⁹ cm⁻³) substrates; and (6) Other substrate combinationswith GaN could be used for demonstration of this device. The methods(1), (2), and (3) result in wurtzite GaN. The use of cubic GaN mayeliminate the polarization charge effects that occur in the wurtzite GaNphase. The possible substrates to grow the GaN collector on may be otherSiC polymorphs or other substrates such as GaN or Si or Sapphire orDiamond or GaAs.

Exemplary Configuration 8: NPN GaAs Emitter-GeSiSn Base-SiC CollectorDouble heterojunction with all dissimilar materials having a smallconduction band offset between Emitter-Base-Collector. This arrangementof materials described herein may combine high transconductance, highbreakdown voltage (SiC collector), and a desirable emitter-baseheterojunction (wide bandgap GaAs emitter on a narrow bandgap GeSiSnhigh conductivity P-type base; GeSiSn can be used as the P-type base).The huge breakdown field of SiC may allow the use of short collectordevices with high bandwidths (cut-off frequency f_(T) and maximumoscillation frequency f_(max)).

A feature of the device described herein is the formation of aheterojunction bipolar transistor, a desirable combination ofsemiconductors for transistors by utilizing a favorable conduction bandalignment between the emitter-base-collector junctions, thus forming aheterojunction bipolar transistor: (1) small conduction band offsetbetween GaAs (emitter)-GeSiSn (base)-SiC (collector); (2) The P-typeGeSiSn base may be lattice matched to N-type GaAs emitter; (3) SiCcollector structure; and (4) Monolithic integration of materials bywafer bonding of GaAs/GeSiSn stack to the N-type SiC collector(circumvents large lattice mismatched growth).

The combination of semiconductors GaAs/GeSiSn stack wafer bonded to SiCfor high performance transistors may have a small conduction band offsetbetween Emitter-Base-Collector. This property allows for the formationof heterojunction transistor structure that can have large gain (largevalence band offset between GaAs and GeSiSn). These materials allow fora low base sheet resistance, low turn-on voltage (GeSiSn has high holemobility and low bandgap energy), and large breakdown voltage (SiC haslarge breakdown electric field strength and high saturated velocity).These material characteristics comprise a useful bipolar transistor.

The GaAs—GeSiSn—SiC stack or GaAs— graded GeSiSn to GeSn—SiC materialsstack is useful for making NPN. FIG. 77 shows an exemplary flat bandenergy diagram of NPN GaAs emitter-GeSiSn base-4H SiC collector 7700stack grown on 4H SiC substrate (energy bandgaps are in parenthesis),with a small conduction band offsets between interfaces and a largevalence band offset at the emitter-base heterojunction. Electrons areeasily injected from the GaAs emitter through the GeSiSn base to the SiCcollector. FIG. 77 shows the conduction band offsets at emitter-base andbase-collector junctions may be less than 0.1 eV, with large valenceband offsets between the GaAs—GeSiSn and GeSiSn—SiC heterojunctions.FIG. 77 shows an exemplary flat band energy diagram of the NPN GaAsEmitter-GeSiSn Base-SiC Collector Double heterojunction with alldissimilar materials having a small conduction band offset betweenEmitter-Base-Collector. Here an emitter up emitter-base stack 7306comprising of an N⁻ emitter GaAs 7301 and a P⁺ base GeSiSn 7302structure. The full monolithic structure can be formed using anepitaxial lift off (ELO) procedure. This emitter-base stack 7306 iswafer bonded to collector 7703 thus forming a wafer bonded junction 7710at the base-collector interface. The wurtzite N⁻ collector 4H SiC 7703can be grown on 4H or 6H (or other variations) sub-collector/substrates.Possible methodologies of wafer bonding this emitter-base stack 7306 tothe collector 7703 is described in Exemplary ELO Wafer BondingConfiguration 6A and in Exemplary Inverted Wafer Bonding Configuration6B. Note the conduction band offset ΔE_(C) may be approximately lessthan 0.1 eV through the NPN HBT structure. The band diagram of this newmaterial structure with a small conduction band offsets betweeninterfaces and a large valence band offset at the emitter-baseheterojunction allows for electrons to be easily injected from the GaAsemitter through the GeSiSn base to the SiC collector.

To form such a structure the interface between the base-emitter stack7306 and the collector 7703 can require wafer bonding, because thelattice constants of the base material and collector material are highlylattice mismatched.

An exemplary structure that could be grown and wafer bonded isillustrated in Table 27.

TABLE 27 Epitaxial Structure of a NPN GaAs—Ge—SiC HBT. Layer Layer NameDescription Comment 1 N⁺ Cap (non-alloyed) 1000 Å InGaAs (Te-doped >10¹⁹cm⁻³) Standard 2 N⁻ Emitter Cap 1500 Å GaAs (Si-doped = 5 × 10¹⁸ cm⁻³)Standard 3 N⁻ Emitter 500 Å GaAs (Si-doped = 3 × 10¹⁷ cm⁻³) Standard 4Base ~500 Å Ge_(1−z)(Si_(0.8)Sn_(0.2))_(z) Latticed matched can beB-doped >10¹⁹ cm⁻³ or 0 < Si % ≤ 40% Can be compositionally 0 ≤ Sn % ≤10% graded GeSiSn—GeSn Thickness range 100 Å-5000 Å 5 N⁻ Collector 10000Å SiC (nitrogen-doped = 1 × 10¹⁶ cm⁻³) Wafer bonded to above 6 N⁺Sub-Collector 5000 Å 4H SiC (5 × 10¹⁸ cm⁻³) Standard (nitrogen doped) 74H SiC (conducting substrate) N+ Substrate: Excellent thermalconductivity Note the dopants listed are only one of many possibledopants, and does preclude the use of other dopants and doping valuesare only nominal values but can take on many variations. The thicknessesare all exemplary and can take on many different values.

FIG. 78 shows an exemplary flat band energy diagram of the NPN GaAsEmitter-GeSi Base-SiC Collector 7800 double HBT with all dissimilarmaterials having a small conduction band offset betweenEmitter-Base-Collector (energy bandgaps are in parenthesis). With smallconduction band offsets between interfaces and a large valence bandoffset at the emitter-base heterojunction electrons can be easilyinjected from the GaAs emitter through the GeSi base to the SiCcollector. Ge_(0.98)Si_(0.02) can be latticed matched to GaAs and mayhave a bandgap energy of 0.7 eV (ranging from 0.67 eV to 0.72 eV). FIG.78 shows conduction band offsets at emitter-base and base-collectorjunctions may be less than 0.1 eV, with large valence band offsetsbetween the GaAs—GeSi and GeSi—SiC heterojunctions. Here an emitter upemitter-base stack 7806 comprising of an N⁻ emitter GaAs 7801 and a P⁺base GeSi 7802 structure. The full monolithic structure can be formedusing an epitaxial lift off (ELO) procedure. This emitter-base stack7806 is wafer bonded to collector 7703 thus forming a wafer bondedjunction 7810 at the base-collector interface. The wurtzite N⁻ collector4H SiC 7703 can be grown on 4H or 6H (or other variations)sub-collector/substrates. Possible methodologies of wafer bonding thisemitter-base stack 7806 to the collector 7703 is described in ExemplaryELO Wafer Bonding Configuration 6A and in Exemplary Inverted WaferBonding Configuration 6B. Note the conduction band offset ΔE_(C) can beless than 0.1 eV through the NPN HBT structure.

To form such a structure the interface between the base-emitter stack7806 and the collector 7703 can require wafer bonding, because thelattice constants of the base material and collector material are highlylattice mismatched.

In other examples, there is a cubic form of SiC that can be used in theHBT device structure. The SiC can be grown face centered cubic (FCC) on3C SiC. SiC in this form can have no polarization charge that degradesthe base-collector performance. SiC (FCC) may also be grown on Sisubstrates or on template substrates that are commercially available.

FIG. 79, shows an exemplary flat band energy diagram of NPN GaAsEmitter-GeSiSn Base-3C SiC collector 7900 stack grown on 3C SiCsubstrate, where the energy bandgaps are in parenthesis. Conduction bandoffsets at emitter-base and base-collector junctions are small, withlarge valence band offsets between the GaAs—GeSiSn and GeSiSn—SiCheterojunctions. Here an emitter up emitter-base stack 7806 comprisingof an N⁻ emitter GaAs 7801 grown on a P⁺ Base GeSiSn 7802 structure. Thefull monolithic structure can be formed using an epitaxial lift off(ELO) procedure. This emitter-base stack 7806 is wafer bonded to SiCcollector 7903 thus forming a wafer bonded junction 7910 at thebase-collector interface. Possible methodologies of wafer bonding thisemitter-base stack 7806 to the collector 7903 is described in ExemplaryELO Wafer Bonding Configuration 6A and in Exemplary Inverted WaferBonding Configuration 6B. Note the conduction band offset ΔE_(C) may be<0.1 eV through the NPN HBT structure. The band diagram of this newmaterial structure with small conduction band offsets between interfacesand a large valence band offset at the emitter-base heterojunctionallows for electrons to be easily injected from the GaAs emitter throughthe GeSiSn base to the SiC collector.

To form such a structure the interface between the base-emitter stack7806 and the collector 7903 can require wafer bonding, because thelattice constants of the base material and collector material are highlylattice mismatched.

It can be useful to put a thin GeSiSn or AlN, AlGaN, InAlN, InN, InGaNlayer down on the SiC to promote adhesion of the wafer bonding of theGeSiSn base. This thin film can be done epitaxially by MOCVD, MBE orPLD.

The base can be linearly or other possible grading, compositionallygraded from GeSiSn to GeSn to have electric field enhancement of thecharge carriers (electrons). Such structure creates an electric fieldthat accelerates the electrons across the base to the collector.

FIG. 80 shows an exemplary flat band energy diagram of the NPN GaAsemitter-graded GeSiSn to GeSn base-SiC collector 8000 HBT. Here avariation of the base up emitter-base stack 8006 comprising a P⁺ basecompositionally graded GeSiSn—GeSn 8002 grown on an N⁻ emitter GaAs 8001layer. The compositionally graded GeSiSn—GeSn 8002 layer can comprise atthe emitter-base interface a lattice matched or near latticed matched orstrained Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) to GaAs, where the GeSiSn may becompositionally graded by reducing the Si content and increasing Gecontent to GeSn at the collector interface. The grading range can gofrom GeSiSn at the emitter-base junction to GeSn at the base-collectorjunction various compositions. This emitter-base stack 8006 is thenwafer bonded with the P⁺ base next to the N⁻ collector SiC 8003 thusforming a wafer bonded junction 8010 at the base-collector interface.Due to the compositional grading of the GeSiSn—GeSn 8002 in the P⁺ base,there is a field enhancement region 8011 that accelerates the carrierstoward the collector. The methodology of wafer bonding the emitter-basestack to the SiC is described in Exemplary Inverted Wafer BondingConfiguration 6B. Note the conduction band offset ΔE_(C) is smallthrough the NPN HBT structure. Note the grade can be linear, stepped,parabolic, or any reasonable variation. Also the graded layer can begrown by one technique such as MOCVD or can comprise of multiple growthdeposition such as but not limited to the MOCVD growth of the GeSiSn.

GaAs Emitter Advantages: (1) The large valence band offset between GaAsemitter and GeSiSn base stops back injection of holes into the emitter.This allows for low n-type doping of the emitter and high p-type dopingof the base, thus lowering base emitter capacitance while stillachieving sizable current gain; (2) GeSiSn may be latticed matched toGaAs which enables dislocation free growth; and (3) The use of AlGaAs ordisordered or ordered InGaP emitter could also be used in this devicestructure.

GeSiSn base may have similar properties to Ge: (1) Ge has a low bandgapwhich results in low turn-on voltage; (2) Ge hole mobility is high andacceptors can be incorporated to high density, thus the base can be madeultra-thin while maintaining a low base sheet resistance which increasescurrent gain and decreases electron transit time; (3) Ge has shallowacceptors, so the hole concentration is generally equal to the acceptordoping level and independent of temperature; (4) The low base sheetresistance results in a high f_(max); (5) The surface recombinationvelocity is low for p-type Ge; and (6) Low resistance ohmic contacts canbe formed on p-type Ge.

SiC Collector Advantages: (1) SiC has many crystalline polymorths. Thecommon ones are hexagonal 4H SiC, 6H SiC, and cubic 3C SiC; (2) 3C cubicSiC has no polarization charge; (3) SiC has high breakdown field whichis excellent for the collector breakdown voltage. SiC may have a smallconduction band offset with GeSiSn, thus no blocking field at theinterface; (4) SiC collector significantly increases the overall thermalconductivity of the material structure; (5) SiC has a high saturationvelocity thus electrons travel without intervalley scattering; and (6)4H SiC power maximum capability is 286 times greater than that of Si.

Exemplary Wafer Bonding of GeSiSn to SiC: The method of wafer bonding ischosen as the most direct means of forming the GeSn to the SiCstructure. Using the method described here, the bonder allows gradualpressure application for the delicate bonding of GeSiSn and SiC. Thelarge size heaters in the plates provide fast temperature ramp up forthe bonding process. The bonder has a self-leveling action to thesurface mechanism and ensures that it is flat with the surface. Also thewafer bonder can be current and voltage biased for anodic wafer bondingor in situ monitoring the current and voltage during the bondingprocess. Table 28 shows basic exemplary wafer bonding process. Also inthe wafer bonding process the top and bottom plates can be biased forvoltage and current to monitor the wafer bonding process to enhance thewafer bonding process (anodic wafer bonding).

TABLE 28 Wafer Bonding Procedure Step Description 1 The wafer is cleavedto appropriate size. 2 Semiconductor materials are thoroughly cleaned. 3Oxides are removed by wet etch. HCl is used for GeSiSn. HF is used forSiC. Then put into methanol. 4 GeSiSn stack material and the SiCmaterial are placed on top of each other and kept in methanol untiltransferred to the wafer bonder. 5 GeSiSn stack and SiC materials areplaced in wafer bonder, which holds the materials together at possibletemperatures of room temperature up to 600° C. for 15 to 60 minutes (butthese can be changed at a pressure between 1 to 10 psi). Typical ambientgas is nitrogen or hydrogen or air or vacuum. 6 The composite structureis slowly cooled and then removed. 7 The composite unit acts as amonolithic structure and is ready for testing.

The wafer bonding allows for independent enhancement of materialswithout regard to lattice matching. It should be noted that GeSiSnlattice constant may be near 5.65 Å and 4H SiC lattice constant is 3.1Å, which is a huge mismatch.

A commonly used metric for comparing various semiconductors is theJohnson's figure of merit (FOM), which compares different semiconductorsfor suitability for high frequency power transistor applications. Table29 shows a comparison of possible Johnson FOM for Si, GaAs, and GaN.

TABLE 29 Comparison of Energy Bandgap, Electron Saturation Velocitiesand Johnson Figure of Merit for Si, GaAs, and GaN. Si GaAs GaN EnergyBandgap (eV) E_(gap) 1.1 1.4 3.4 Peak Electron Saturation Velocity 1 ×10⁷ 1.9 × 10⁷ 2.5 × 10⁷ (cm/s) V_(sat peak) Normalized Johnson FOM 1  9.5 572    Johnson Figure of Merit = Maximum power × frequency = P_(max)× f ≈ (E_(gap) ⁴ × V_(sat peak) ²)

Table 30 shows a comparison of possible Johnson FOM for 3C SiC, 4H SiC,and 6H SiC.

TABLE 30 Comparison of Energy Bandgap, Electron Saturation Velocitiesand Johnson Figure of Merit for 3C SiC, 4H SiC and 6H SiC. 3C SiC 4H SiC6H SiC Energy Bandgap (eV) E_(gap) 2.4 3.2 3.0 Peak Electron SaturationVelocity 2 × 10⁷ 2 × 10⁷ 2 × 10⁷ (cm/s) V_(sat peak) Normalized JohnsonFigure of Merit 91 286 221 Johnson Figure of Merit = Maximum power ×frequency = P_(max) × f ≈ (E_(gap) ⁴ × V_(sat peak) ²)

Interface defect formation: Thermal expansion coefficients of exemplarymaterials are shown in Table 31. Due to the fact thermal expansioncoefficients of all the materials are similar, the thermal stressgenerated during low temperature wafer bonding should be minimal.

TABLE 31 Thermal Expansion Coefficients. Material Thermal ExpansionCoefficient (10⁻⁶ K⁻¹) @ 300 K GaAs 6.0 Ge 5.9 GaN 5.6 3C SiC 3.8 4H SiC4.3 6H SiC 4.3

Table 32 shows thermal conductivities of the various semiconductors. SiChas high thermal conductivities.

TABLE 32 Thermal Conductivities of Semiconductors. Material ThermalConductivity (Wcm⁻¹ K⁻¹) @ 300 K GaAs 0.55 Ge 0.58 GaN 1.3 3C SiC 3.6 4HSiC 3.7 6H SiC 4.9 Diamond 8.9-13.5

Exemplary Configuration 9: NPN GaAs Emitter-GeSiSn Base-ZnSe CollectorDouble heterojunction with all dissimilar materials. The deviceelucidated in this example can include a asymmetric doubleheterojunction GaAs—GeSiSn—ZnSe HBT device. This device can havedesirable base characteristics with a low voltage base turn-on (<1.0 V)region and a symmetric heterojunction thus eliminating the offsetvoltage in the transistor output characteristic that reduces power addedefficiency. FIG. 81 illustrates an exemplary flat band energy diagram ofthe material structure. This device can be desirable for high speed andRF (radio frequency) power amplification. This material is near latticedmatched thus making it a useful structure for crystal growth techniques.

The monolithic GaAs—GeSiSn—ZnSe double HBT may have a favorableconduction band alignment. This transistor structure can have large gain(large valence band offset between GaAs and GeSiSn). These materialsallow for a low base sheet resistance, low turn-on voltage (GeSiSn hashigh hole mobility and low bandgap energy), and large breakdown voltage(ZnSe has large breakdown electric field strength and high saturatedvelocity). These material characteristics make for a useful bipolartransistor.

FIG. 81 shows an exemplary flat band energy diagram of the NPN GaAsEmitter-GeSiSn Base-ZnSe Collector 8100 HBT with possibly favorableelectron transport conduction band offsets between interfaces and alarge valence band offset at the emitter-base heterojunction. Electronsmay be injected from the GaAs emitter through the GeSiSn base to theZnSe collector. FIG. 81 shows the conduction band offsets atemitter-base junction are small, with large valence band offsets betweenthe GaAs—GeSiSn and GeSn—ZnSe heterojunctions. Here the emittercomprising of an N⁻ GaAs 8101 and a P⁺ base GeSn 8102 structure, with alarge bandgap energy N⁻ collector ZnSe 8103

FIG. 82 shows an exemplary schematic embodiment of an NPNGaAs—GeSiSn—ZnSe double HBT 8200 in a mesa configuration. Note thisstructure could be grown inverted thus one could start the growth usingGaAs substrates and finish with the ZnSe collector and sub-collector.Note that this can be a vertical device, which can be desirable forpower applications because the lateral area can be minimized. FIG. 82shows a general configuration of a GaAs—GeSiSn—ZnSe heterojunctionbipolar transistor as a vertical stack geometry. Typically the structurecan be grown epitaxially or by various means. For a verticalheterojunction bipolar transistor, typically a semi-insulating ZnSesubstrate 8201 is used as the seed crystal to start the growth of thestructure. A highly conducting N⁺ ZnSe sub-collector 8202 is then grown,followed by a low doped N⁻ ZnSe collector 8203. A P⁺ GeSiSn base 8204 isthen grown, followed by a GaAs emitter 8205, and finally a highlyconducting GaAs contact layer 8206. Electrical contact is made to devicevia the metalized contact pads: emitter contact 8210, base contact 8211,and collector contact 8212. The voltages and currents are applied to thedevice via the contact pads. Vertical configuration offers someadvantages.

The base can be linearly or other possible grading, compositionallygraded from GeSiSn to GeSn to have electric field enhancement of thecharge carrier electrons. The compositionally graded GeSiSn—GeSn 8302layer can comprise at the emitter-base interface a lattice matched ornear latticed matched or strained Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) toGaAs, where the GeSiSn may be compositionally graded by reducing the Sicontent and increasing Ge content to GeSn at the collector interface.The grading range can go from GeSiSn at the emitter-base junction toGeSn at the base-collector junction at various compositions.

FIG. 83 shows an exemplary flat band energy diagram of the NPN GaAsemitter-graded GeSiSn to GeSn base-ZnSe collector HBT 8300. Thecompositionally graded Ge—GeSn 8302 layer can comprise at the emitterinterface starting with Ge or a low Sn % GeSn layer which may be gradedadding more Sn % to the GeSn at the collector interface. Thecompositional grading range can go from Ge at the emitter to GeSn atvarious compositions up to 20%. Due to the compositional grading of theGeSiSn—GeSn 8302 in the P⁺ base, there is a field enhancement region8311 that accelerates the carriers from emitter GaAs 8301 toward thecollector ZnSe 8303. Note the grade can be linear, stepped, parabolic,or any reasonable variation. Also the graded layer can be grown by onetechnique such as MOCVD or can comprise multiple growth deposition suchas but not limited to the MOCVD growth of the Ge and the subsequent PLDgrowth of the GeSn layer.

Table 33 shows an exemplary structure that could be grown.

TABLE 33 Epitaxial Structure of NPN GaAs—GeSiSn—ZnSe HBT. Layer LayerName Description Comment 1 N⁺ Cap (non-alloyed) ~1000 Å InGaAs (Te-doped>10¹⁹ cm⁻³) Te = tellurium InGaAs layer is relaxed 2 N⁻ Emitter Cap~1500 Å GaAs (Si-doped ~5 × 10¹⁸ cm⁻³) Si = silicon 3 N⁻ Emitter ~500 ÅGaAs (Si-doped = ~3 × 10¹⁷ cm⁻³) 4 P⁺ Base ~500 ÅGe_(1−z)(Si_(0.8)Sn_(0.2))_(z) Latticed matched can be B-doped >10¹⁹cm⁻³ or 0 < Si % ≤ 40% Can be compositionally 0 ≤ Sn % ≤ 10% gradedGeSiSn—GeSn Thickness range 100 Å-5000 Å 5 N⁻ Collector ~10,000 Å ZnSe(doped ~1 × 10¹⁶ cm⁻³) Chlorine doped 6 N⁺ Sub-Collector ~5000 Å ZnSe(doped ~5 × 10¹⁸ cm⁻³) Chlorine doped 7 High Purity Buffer ~500 Å ZnSe(un-doped) No doping 8 ZnSe semi-insulating substrate Note the dopantslisted are only one of many possible dopants, and does preclude the useof other dopants and doping values are only nominal values but can takeon many variations. The thicknesses are all exemplary and can take onmany different values.

Exemplary Configuration 10: Si Emitter-SiGe base with GeSn quantumwell-SiGe Collector-Si sub-collector double light emittingheterojunction transistor laser or LED for Si photonics. Theintroduction of a GeSn quantum well or quantum dot or Ge quantum dotinto a standard SiGe HBT design allows for the novel development of a Siphotonic transistor laser. SiGe has a wide range of bandgaps from astarting point of Si with a bandgap energy of 1.1 eV, atSi_(0.8)Ge_(0.siSn Ba2) has a bandgap energy of approximately 1 eV, atSi_(0.6)Ge_(0.4) has a bandgap energy of approximately 0ge.93 eV, and atSi_(0.2)Ge_(0.8) has a bandgap energy of approximately 0.87 eV. Tofabricate a light emitting bipolar transistor the following flat banddiagram is shown for an n-p-n device. Inserted into the SiGe base is aGeSn quantum well or quantum dot or Ge quantum dot.

FIG. 84 shows an exemplary flat band energy diagram of a separateconfinement heterostructure (SCH) laser diode device utilizing a GeSn QWor QD region with UID GeSiSn Barrier/OCL region 8400. The QW or QD arelocated in UID GeSiSn barrier/OCL layer 8403 & 8405 region with PSi_(0.8)Ge_(0.2) 8402 cladding and N Si_(0.8)Ge_(0.2) 8406 claddinglayers. This structure represents a PN junction or diode with anunintentionally doped (UID) active region and optical confinement regionbetween the P Si_(0.8)Ge_(0.2) 8402 cladding and N Si_(0.8)Ge_(0.2) 8406cladding. The UID Ge 8403 and 8405 forms the barrier material for theGeSn QW or QD 8404 active region. The combination of the barrier andactive region forms the waveguide 8408 of the laser. The P⁺ Si 8401layer serves for injection of the holes into the device. The N⁺ Si 8407layer serves for injection of the electrons into the device. Thecarriers are collected in the waveguide region and recombine in the GeSnQW or QD 8404 active region to generate light. Thus it is called anelectrical injection laser. Though this depicts a symmetric structure itcan be also asymmetric.

A further innovation is to take the SCH laser structure and form atransistor laser structure.

FIG. 85 shows an exemplary flat band energy diagram of a SiEmitter-GeSiSn Base/Barrier with GeSn QW or QD-SiGe Collector transistorlaser 8500. The transistor laser includes a GeSn QW or QD 8504 activeregion inserted into a SiGeSn P⁺ base/barrier 8503 & 8505. This HBTlaser is grown on Si substrates, thus compatible with Si processing. TheGeSiSn forms the P⁺ base and also acts as a barrier layer for quantumconfinement of the electrons and holes in the GeSn QW or QD 8504. TheSi_(0.8)Ge_(0.2) 8506 collector can be part of the waveguide 8508. TheGeSn QW or QD 8504 inserted into a base/barrier serves for thecollection region for electrons and holes to recombine to generatelight. The P⁺ base SiGeSn 8503 & 8505 and the Si_(0.8)Ge_(0.2) N⁻collector 8506 serve as the optical confinement layer and the waveguide8508 material. The Si emitter cladding 8502 & Si sub-collector cladding8507 serve as the cladding layers for this structure. The claddingserves as funneling carriers into the active waveguide 8508 region andtraps the emitted light in the waveguide structure.

Table 34 shows an exemplary structure that could be grown for theepitaxial structure of NPN light emitting Si—GeSn—SiGe HBT. Note thebase QW well could also be compressively strained.

TABLE 34 Epitaxial Structure of NPN light emitting Si—GeSn—SiGe HBT.Layer Layer Name Description Comment 1 N⁺ Cap ~2000 Å Si (As-doped >10¹⁹cm⁻³) As = Arsenic 2 N⁻ Emitter Contact ~5000 Å Si (As-doped = 5 × 10¹⁸cm⁻³) Cladding 3 N⁻ Emitter ~1000 Å Si (As-doped = 5 × 10¹⁷ cm⁻³)Cladding Undoped-layer ~50 Å Si_(0.8)Ge_(0.2) Intrinsic layer 4 P⁺ Base~1000 Å GeSiSn (p-doped: B >10¹⁹ cm⁻³) B = Boron QW ~10-1000 ÅGe_(0.9)Sn_(0.1) QW 0 < Sn % < 20 or QD or ~10-500 Å GeSn quantum dotLight emission ~1000-5000 nm P⁺ Base ~200 Å GeSiSn (p-doped: B >10¹⁹cm⁻³) B = Boron Undoped-layer ~50 Å Si_(0.8)Ge_(0.2) Intrinsic layer 5N⁻ Collector ~1200 Å Si_(0.8)Ge_(0.2) (As-doped ~5 × 10¹⁵ cm⁻³) 6 N⁺Sub-Collector ~6000 Å Si (As-doped ~1 × 10¹⁹ cm⁻³) Cladding 7 N⁺ Buffer~500 Å Si (As-doped) 8 N⁺ Si conducting substrate Note for thisstructure a variety of compositions of the SiGe can be used (0% to 80%Ge %)

The front and back cleaved facets form the mirror of the laser.Anti-reflection coating can be put on the facets to provide for a betterresonant cavity. Then metallizing the top and bottom of the transistorstructure with an aperture open in the top or bottom metal would allowfor the light to leave.

FIG. 86 shows a possible exemplary cross-sectional device depiction ofan NPN Si based edge emitting transistor laser or LET 8600. Note in thisschematic embodiment the GeSn QW could be replaced by a GeSn quantum dotor Ge quantum dot. Typical quantum dot sizes are 1 to 50 nm. Note thevertical configuration could also be possible by putting dielectric orsuperlattice mirrors on top of the Si contact layer and the bottom ofthe Si substrate. The transistor laser includes a GeSn QW 8604 activeregion inserted into a GeSiSn 8603 & 8605 P⁺ base/barrier of the HBT.The laser can require a resonant cavity to get optical gain, andtypically this can be formed from the front 8611 and back cleaved facets8610 of the semiconductor crystal wafer. The structure can be grown onN⁺ Si conducting substrate 8608, which is the seed crystal to grow thefull structure. An N⁺ Si sub-collector/cladding 8607 is grown on thesubstrate. An N⁻ Si_(0.8)Ge_(0.2) collector 8606 which also forms a partof the waveguide is grown on the sub-collector. The N⁻ Siemitter/cladding 8602 and the N⁺ Si sub-collector/cladding 8607 do dualfunctions of optical confinement of the light 8609 produced from theactive region GeSn QW 8604 and controlling the flow of electrons andholes into the active region. The P⁺ GeSiSn base 8605 & 8603 form thebarrier material for the GeSn QW 8604, and also provide the waveguidematerial. The laser can require a resonant cavity to get optical gain,and typically this can be formed from the front cleaved facets 8611 andback cleaved facets 8610 of the semiconductor crystalline structure.Layer 8600 is the highly conductive N⁺ Si contact layer. Layer 8601 isthe highly conductive N⁺ Si emitter contact layer.

There are atmospheric transmission windows and this type of transistorlaser structure can be useful for developing cost effective Si basedphotonic devices for telecommunications applications. Such a device canbe useful on-chip or chip to chip communications.

Crystal growth modification of interfaces of the materials prior towafer bonding for enhancing wafer bonding quality. The crystal growingtechniques to grow the device structure in the patent are well known inthe literature. The various techniques such as Metalorganic ChemicalVapor Depostion (MOCVD), Molecular beam epitaxy (MBE), Vapor PhaseEpitaxy (VPE), Liquid Phase Epitaxy (LPE), etc., can grow variousepitaxial structures and can be used for interface modification of thewafer bonding procedure. An exemplary description of pulsed laserdeposition is used to describe modification of interfaces for waferbonding of two crystals.

Pulsed laser deposition (PLD) epitaxy is a crystal methodology to formsingle layers on a suitable substrate. The system comprises of a targetholder and a substrate holder housed in a vacuum chamber. A pulsedNd-YAG laser, eximer laser, etc., beam is directed toward a sourcetarget, which vaporizes the source (laser ablation), and creates a beamof source particles (plasma plume) for deposition onto heated substrate.

For an exemplary situation for wafer bonding GeSiSn to GaN or SiC, athin layer of GeSn may be deposited on the GeSiSn or other materials canbe deposited by PLD to promote adhesion and better interface formationon one or both of the layers to be wafer bonded. To promote interfacewafer bonding InAlN, InGaN, AlN, AlGaN, InN could be deposited on theGaN or SiC to promote adhesion and electrical junction quality. Onecould deposit ZnSe to change the band bending or as a method forneutralizing the piezoelectric charge that can occur in wurzite GaN orSiC heterostructures.

FIG. 87 shows a possible exemplary method of using epitaxial depositedlayer to promote adhesion and the formation of a heterojunction.Possible epitaxial methods may include PLD or MBE or MOCVD or LPE. Inthis situation thin adhesion layers are applied to both materials but itcan also be possible to apply the adhesion layer to only one of thematerials. The adhesion layers can be the same or different depending onapplication. SiC has a strong oxide and adding adhesion layers may formmaterials with electrical and adhesion properties that promote theheterojunction formation. The epitaxial techniques can also be used todeposit quantum wells, quantum dots and all variety of epitaxialstructures on materials that are difficult to grow on.

In this exemplary example, FIG. 87 shows GeSn 8705 could be deposited onGeSiSn 8707 by PLD. In this exemplary case InAlN 8706 could be depositedfor example by PLD on the GaN 8708. The GeSiSn 8707 with GeSn at itssurface may be the first bonding material. The GaN 8708 with InGaN atits surface may be the second bonding material Step 8700 shows that bothmaterials are oriented with their modified surfaces toward each other.Step 8701 shows that the modified surface GeSiSn 8707 is placed on themodified surface of the GaN 8708, with the modified interfaces incontact. This structure is placed in the wafer bonder with wafer bondertop plate 8710 and wafer bonder bottom plate 8711 clamping thestructure. With application of heat 8712 and pressure applied 8713 andover time the two structures 8707 and 8708 can be wafer bonded together.This wafer bonding process can also occur at room temperature. Step 8702shows the final monolithic structure. The conditions of wafer bondinginclude the amount of pressure between the top and bottom plates of thebonder or use of gas ambient in the bonding process, and other possibleconditions.

Exemplary Configuration 11: Another embodiment represents a possible wayof integrating an InGaP emitter (lattice matched or near latticedmatched to GaAs)—GaAs base-GaN collector HBT. The InGaP—GaAs stack waferbonded to the GaN collector makes for an ideal heterojunction bipolartransistor. The InGaP—GaAs—GaN stack may have a near-zero conduction(less than 0.1 eV) band offset throughout the layers from emitter tobase to collector, which may be ideal for electron transport in an NPNheterojunction bipolar transistor.

FIG. 88 shows the exemplary flat band energy band diagram showing theenergy band alignments of NPN InGaP Emitter-GaAs Base-GaN Collector HBT8800, where the vertical axis is Energy (eV) 2310 and the horizontal isthe Distance (A.U.) 2311. The approximate band gap energies are shown inparenthesis for the corresponding material. This device structure mayhave a small conduction band offsets between emitter-base-collectorinterfaces and a large valence band offset at the emitter-base and basecollector heterojunction. Electrons can be easily injected from theInGaP 8802 emitter through the GaAs 8803 base to the GaN 8804 collector.Conduction band offset at emitter-base may be ΔE_(C)<0.1 eV 8806 and theconduction band offset at base-collector junctions may be ΔE_(C)<0.1 eV8807, with large valence band offsets between the InGaP—GaAs (ΔE_(V)8808) and GaAs—GaN (ΔE_(V) 8809) heterojunctions. The band alignmentsmay be desirable for high performance NPN HBTs. An emitter-base stack8805 comprising N⁻ emitter InGaP 8802 on P⁺ Base GaAs 8803 structure canbe wafer bonded to the GaN 8804 collector. The InGaP 8802 should have asmall conduction band offset ΔE_(C) 8807 with the GaAs 8803. Thisemitter-base stack 8805 may be wafer bonded to the N⁻ collector GaN 8804thus forming a wafer bonded junction 8801 at the base-collectorinterface. The GaN 8804 may have a small conduction band offset ΔE_(C)8808 with the GaAs 8803. Note the conduction band offset ΔE_(C) may besmall <0.1 eV through the NPN HBT structure.

InGaP semiconductor can be grown epitaxially and latticed matched toGaAs at the composition In_(0.49)Ga_(0.51)P. If typically grown at hightemperatures, it can grow in an ordered phase where the crystallinestructure forms sheets of In—P and Ga—P atoms can alternate in the (001)planes of the FCC unit cell without the intermixing of the Ga and Inatoms on the lattice planes. The ordered InGaP results in an almost zeroconduction band discontinuity between the InGaP and GaAs and is calledthe ordered phase (this can be of weakly type I or weakly type IIbecause it is close to zero) which may be approximately <0.1 eV for theordered phase. With different growth conditions, the In and Ga atoms canintermix and the disordered InGaP phase can form, which has anapproximate conduction band offset <0.2 eV. In either case theconduction band offset of InGaP to GaAs may be small.

The exemplary structure is shown in Table 35 of the wafer bondedInGaP—GaAs—GaN HBT.

TABLE 35 Exemplary Structure of Wafer Bonded NPN InGaP—GaAs—GaN HBT.Layer Layer Name Description Comment 1 N⁺ Cap ~1000 Å InGaAs (Te-doped>10¹⁹ cm⁻³) 2 N− Emitter Cap ~1500 Å GaAs (Si-doped ~5 × 10¹⁸ cm⁻³) 3 N−Emitter ~500 Å InGaP (Si-doped ~3 × 10¹⁷ cm⁻³) Ordered or disordered ormixed 4 P⁺ Base ~1000 Å GaAs Thickness range 100 Å-5000 Å 5 N− Collector~10000 Å GaN (Si-doped ~1 × 10¹⁶ cm⁻³) Wafer bonded to above 6 N⁺Sub-Collector ~5000 Å GaN (Si-doped ~5 × 10¹⁸ cm⁻³) 7 Substrate 4H SiCsubstrate Crystalline The substrate may be other SiC polymorphs or othersubstrates such as GaN or Si or Sapphire or Diamond or GaAs.

The InGaP—GaAs—GaN may have a near-zero conduction band offset (lessthan 0.1 eV) throughout the layers, which may be useful for an NPNbipolar transistor. FIG. 89 shows a possible exemplary cross-sectiondevice depiction of the wafer bonded InGaP—GaAs—GaN NPN HBT 8920 in amesa configuration. Note that this is a vertical device, which may bedesirable for power applications because the lateral area can beminimized. The NPN HBT comprises an emitter base stack 8921 with a waferbond 8931 to the GaN structure 8940 to form the monolithic device. Theemitter base stack 8921 consists of a N+ GaAs 8922 on top of N⁻ InGaP8923 emitter, followed by a P+ GaAs base 8924. The emitter 8926 metalmakes ohmic contact with the N+ GaAs 8922 layer. The base 8925 metalmakes ohmic contact to the P+ GaAs Base 8924. The GaN structure 8940 cancomprise a variety of forms, but for an exemplary case the GaN is grownon a 4H SiC substrate 8927, though a GaN or sapphire or Si or GaAs ordiamond substrate could also be used. Starting with an intrinsic 4H SiCsubstrate 8927 then a N⁺ Conducting GaN 8928 layer is grown to which aN− GaN collector 8929 is grown. The collector 8930 metal makes ohmiccontact with N+ Conducting GaN 8928. The GaN structure 8940 is waferbonded to the Emitter Base Stack 8921.

To summarize, the devices are fabricated using standard semiconductorprocess techniques. For the PN junction fabrication, a single mask levelfor the etching of the base and ohmic anneals is used. The process usesmesa wet-etch and metallization lift off techniques common in HBTfabrication. AuGeNiAu or other metals can be used for the N-type GaAsmaterials and Al to P-type GeSiSn. The junctions of interest are theemitter-base junction and the base-collector junction.

Exemplary Embodiment

Base region with all the above compositional GeSiSn—GeSn gradingvariations of the base from emitter side to collector side.

Exemplary Embodiment

Base region including all the variations and inclusion of a GeSn quantumwell or GeSn quantum dot structure in the base region making a lightemitting transistor laser.

Exemplary Summary of HBT Parameters

The embodiments described herein can relate to the following: anybipolar transistor using a Ge base; GeSn base; GeSiSn base; a GeSi base;any bipolar transistor using a compositionally graded GeSiSn—GeSn base;and/or any light emitting bipolar transistor laser using a GeSn activeregion which can include a GeSn quantum well or GeSn quantum dot in thebase region.

Exemplary Summary of transistor laser or LET Parameters: The embodimentsdescribed herein can relate to the following: any light emitting bipolartransistor laser using a GeSiSn active region which can include a GeSiSnquantum well or GeSiSn quantum dot in the base region, where thebarrier/OCL may be GeSiSn layers.

Note through out the context of the document Ge_(1-x-y)Si_(x)Sn_(y) maybe referred to as GeSiSn. It should be noted where the subscripts aremissing GeSiSn refers to Ge_(1-x-y)Si_(x)Sn_(y), GeSi refers toGe_(1-a)Si_(a), GeSn refers to Ge_(1-b)Sn_(b), and SiSn refers toSi_(1-c)Sn_(c). Ge_(1-x-y)Si_(x)Sn_(y). Note that Ge_(1-x-y)Si_(x)Sn_(y)may at various compositions be lattice matched to the lattice constantsof GaAs and Ge semiconductors. Here y can vary from 0≤y≤0.1, and x canvary 0<x≤0.4. Ge_(1-x-y)Si_(x)Sn_(y) can be comprised materials of Ge,Ge_(1-a)Si_(a), Ge_(1-b)Sn_(b), and Si_(1-c)Sn_(c) at variouscompositions which may also be latticed matched or near latticed matchedor strained to GaAs or Ge. GeSiSn may be also written in the followingform Ge_(1-z)(Si_(1-k)Sn_(k))_(z). Where the value of k may be equal to0.2 or near that value and have a range of values 0.1≤k≤0.4 and where zhas a range of 0<z≤0.5. However for the GeSiSn latticed matched orcoherently strained to GaAs or Ge there may be a range of values that kcan have, which may be close to 0.2. It may be possible to write GeSiSnlatticed matched or near latticed matched or strained to GaAs or Ge asGe_(1-z)(Si_(0.8)Sn_(0.2))_(z). In this designation the subscripts underthe Si_(0.8) and Sn_(0.2) may be empirical values and can have a degreeof variation as given by 0.1≤k≤0.4 in Ge_(1-z)(Si_(1-k)Sn_(k))_(z). Thisform may be useful for the following materials compositionGe_(1-z)(Si_(0.8)Sn_(0.2))_(z) where z is 0<z≤0.5, which may result inthat Ge_(1-z)(Si_(0.8)Sn_(0.2))_(z) may be lattice matched or nearlatticed matched or pseudomorphic to Ge or GaAs semiconductors. ThusGeSiSn has a range of Si and Sn for the lattice matched condition toGaAs and Ge. Here the lattice constant of GaAs and Ge may be about 5.65Å. The lattice mismatch between Ge and GaAs may be less than about 0.1%which may be considered near-latticed matched or lattice matched. AlsoGeSiSn when grown on GaAs or Ge may be tensile or compressivelystrained, which may be useful in devices. Sometimes for strained GeSiSnthe term pseudomorphic may be used. GeSi designated by Ge_(1-a)Si_(a)may also be latticed matched or near lattice matched or coherentlystrained to GaAs or Ge. Here the value of a may be about 0.02, with arange of variation of 0.0<a≤0.03. Thus the designation forGe_(0.98)Si_(0.02) may represent GeSi lattice matched or near latticedmatched or coherently strained to GaAs or Ge. In this designation thesubscripts under the Ge_(0.98) and Si_(0.02) may be empirical values andcan have a degree of variation as given by 0.0<a≤0.3 in Ge_(1-a)Si_(a).The materials of Ge, Ge_(1-a)Si_(a), Ge_(1-b)Sn_(b), and Si_(1-c)Sn_(c)may be interchanged with Ge_(1-x-y)Si_(x)Sn_(y) materials system for avariation of the embodiments of the devices elucidated. It should benoted where the subscripts are missing GeSiSn refers toGe_(1-x-y)Si_(x)Sn_(y), GeSi refers to Ge_(1-a)Si_(a), GeSn refers toGe_(1-b)Sn_(b), and SiSn refers to Si_(1-c)Sn_(c). This terminologyrefers to the fact that alloy semiconductor GeSiSn consists of thefollowing component materials GeSi, GeSn and SiSn at various possiblecompositions. Also it should be noted for GeSiSn where the Sn content iszero, GeSi can be grown latticed or near latticed matched to GaAs andGe. This value may be close to the composition Ge_(0.98)Si_(0.02).Throughout the context of the document Ge_(1-x-y)Si_(x)Sn_(y) may bereferred to as GeSiSn. Also the term graded or grading refers tocompositional grading of the semiconductor alloy.

It should be noted that the values of the bandgap energies can changedue to growth conditions and other factors. The values of the conductionand valence band offsets between dissimilar heterojunctionsemiconductors are used as guidelines and can be different dependent onthe growth conditions, doping levels, and other factors. Theseparameters are also dependent on the temperature of the materials.

Although the embodiments have been described with reference to specificembodiments, it is understood by those skilled in the art that variouschanges can be made without departing from the spirit or scope of theinvention. Accordingly, the disclosure of embodiments of the inventionis intended to be illustrative of the scope of the invention and is notintended to be limiting. It is intended that the scope of the inventionshall be limited only to the extent required by the appended claims. Forexample, to one of ordinary skill in the art, it is readily apparentthat the methods, processes, and activities described herein may becomprised of many different activities, procedures and be performed bymany different modules, in many different orders that any element of thefigures may be modified and that the foregoing discussion of certain ofthese embodiments does not necessarily represent a complete descriptionof all possible embodiments.

All elements claimed in any particular claim are essential to theembodiment claimed in that particular claim. Consequently, replacementof one or more claimed elements constitutes reconstruction and notrepair. Benefits, other advantages, and solutions to problems have beendescribed with regard to specific embodiments. The benefits, advantages,solutions to problems, and any element or elements that may cause anybenefit, advantage, or solution to occur or become more pronounced,however, are not to be construed as critical, required, or essentialfeatures or elements of any or all of the claims, unless such benefits,advantages, solutions, or elements are stated in such claim.

Moreover, embodiments and limitations disclosed herein are not dedicatedto the public under the doctrine of dedication if the embodiments and/orlimitations: (1) are not expressly claimed in the claims; and (2) are orare potentially equivalents of express elements and/or limitations inthe claims under the doctrine of equivalents.

The invention claimed is:
 1. A transistor comprising: a GeSiSn baseregion; an emitter region; and a collector region, wherein: thetransistor is a heterojunction bipolar transistor; and the GeSiSn baseregion comprises a Sn content and a Si content to be latticed matched orcoherently strained to GaAs.
 2. The transistor of claim 1, wherein theheterojunction bipolar transistor is an NPN device.
 3. The transistor ofclaim 1, wherein the GeSiSn base region comprises a compositionallygraded GeSiSn—GeSn.
 4. The transistor of claim 1, wherein: the emittercomprises GaAs; and the collector comprises GaAs.
 5. The transistor ofclaim 1, wherein: the emitter comprises InGaP; and the collectorcomprising GaAs.
 6. The transistor of claim 1, wherein: the emittercomprises AlGaAs; and the collector comprises GaAs.
 7. The transistor ofclaim 1, wherein: the emitter comprises GaAs; and the collectorcomprises GaN.
 8. The transistor of claim 1, wherein: the emittercomprises GaAs; and the collector comprises SiC.
 9. The transistor ofclaim 1, wherein: the emitter comprises InGaP; and the collectorcomprises GaN.
 10. The transistor of claim 1, wherein the GeSiSn baseregion comprises compressively strained GeSiSn.
 11. The transistor ofclaim 1, wherein the GeSiSn base region comprises tensile strainedGeSiSn.
 12. The transistor of claim 1, wherein the GeSiSn base regioncomprises relaxed GeSiSn.
 13. The transistor of claim 1, wherein thetransistor is a heterojunction bipolar transistor and is a wafer bondedheterojunction bipolar transistor.
 14. A transistor comprising: a GeSiSnbase region; an emitter region; and a collector region, wherein: thetransistor is a heterojunction bipolar transistor; and the collectorcomprises GaN and is wafer bonded to the GeSiSn base region.
 15. Atransistor comprising: a GeSiSn base region; an emitter region; and acollector region, wherein: the transistor is a heterojunction bipolartransistor; and the collector comprises SiC and is wafer bonded to theGeSiSn base region.